Imidazopyridine compounds as 5-HT4 receptor agonists

ABSTRACT

This invention provides a compound of the formula (I):  
                 
 
     or a pharmaceutically acceptable salt thereof, wherein 
     R 1  represents a hydrogen atom or a halogen atom;  
     R 2  represents a methyl group or an ethyl group;  
     R 3  represents a branched alkyl group having from 3 to 6 carbon atoms or an alkyl group having from 3 to 6 carbon atoms substituted by an alkoxy group having from 1 to 6 carbon atoms;  
     with the proviso that when the terminal carbon atom of said alkyl group of R 3  is substituted by said alkoxy group, said alkyl group is a branched alkyl group. 
     These compounds have 5-HT 4  receptor binding activity, and thus are useful for the treatment of gastroesophageal reflux disease, non-ulcer dyspepsia, functional dyspepsia, irritable bowel syndrome or the like in mammalian, especially humans. This invention also provides a pharmaceutical composition comprising the above compound.

RELATED APPLICATIONS

[0001] This application claims benefit of priority under 35 U.S.C 119(e)to U.S. Provisional Application No. 60/412,485 filed on Sep. 20, 2002,which is herein incorporated in its entirety by reference.

TECHNICAL FIELD

[0002] This invention relates to novel imidazopyridine compounds. Thesecompounds have 5-HT₄ receptor agonist binding activity, and thus areuseful for the treatment of or prevention of gastroesophageal refluxdisease, gastrointestinal disease, gastric motility disorder, non-ulcerdyspepsia, functional dyspepsia, irritable bowel syndrome, constipation,dyspepsia, esophagitis, gastroesophageral disease, nausea, centralnervous system disease, alzheimers disease, cognitive disorder, emesis,migraine, neurological disease, pain, ischaemic stroke, anxiety,cardiovascular disorder or the like, in mammalian, especially human. Thepresent invention also relates to a pharmaceutical compositioncomprising the above compounds.

BACKGROUND ART

[0003] Serotonin (5-HT) receptors are known to have a plurality ofsubtypes such as 5-HT₁, 5-HT₂, 5-HT₃ and 5-HT₄. These 5-HT₄ receptorsare disclosed in, for example, European Journal of Pharmacology 146(1988), 187-188, and Naunyn-Schmiedeberg's Arch. Pharmacol. (1989)340:403-410.

[0004] 5-HT₄ receptor modulators (e.g., agonists and antagonists) arefound to be useful for the treatment of a variety of diseases such asgastroesophageal reflux disease, gastrointestinal disease, gastricmotility disorder, non-ulcer dyspepsia, functional dyspepsia, irritablebowel syndrome, constipation, dyspepsia, esophagitis, gastroesophageraldisease, nausea, central nervous system disease, alzheimers disease,cognitive disorder, emesis, migraine, neurological disease, pain, andcardiovascular disorders such as cardiac failure and heart arryhthmia(See TiPs, 1992, 13, 141; Ford A. P. D. W. et al., Med. Res. Rev., 1993,13, 633; Gullikson G. W. et al., Drug Dev. Res., 1992, 26, 405; RichardM. Eglen et al, TiPS, 1995, 16, 391; Bockaert J. Et al., CNS Drugs, 1,6; Romanelli M. N. et al., Arzheim Forsch./Drug Res., 1993, 43, 913;Kaumann A. et al., Naunyn-Schmiedeberg's. 1991, 344, 150; and RomanelliM. N. et al., Arzheim Forsch./Drug Res., 1993, 43, 913).

[0005] A variety of imidazopyridine compounds have been known as 5HTreceptor antagonists or agonists. For example, Japanese PatentPublication Laid-Open No. H01-258,674 and H02-643,274 discloseimidazopyridine compounds as 5HT receptor antagonists. WO 96/05166discloses imidazopyridine compounds as 5HT₄ agonists. WO92/15593; U.S.Pat. No. 5,260,303; U.S. Pat. No. 5,604,239; U.S. Pat. No. 5,591,749;U.S. Pat. No. 5,219,850; U.S. Pat. No. 5,434,161; U.S. Pat. No.5,137,893; U.S. Pat. No. 5,196,547; and EP 504679 describe a variety ofimidazopyridine compounds as 5HT₃ receptor antagonists. WO94/08998discloses imidazopyridine compounds as 5HT₄ receptor antagonists.

[0006] Also, imidazopyridine compounds synthesized for different usesare described in JP2001/6877; WO01/5763; WO 99/50247; WO 97/27852, WO9738665 and EP 274867.

[0007] It would be desirable if there were provided 5HT₄ receptoragonists which have more 5HT₄ receptor agonist activities.

[0008] A variety of imidazopyridine 5-HT₄ receptor modulators compoundswere disclosed in U.S. Application No. 60/343,371, filed on Oct. 22,2001. Especially, compounds represented by the following formula isdisclosed in U.S. Application No. 60/343,371:

[0009] QT prolongation is known to have a potential liability to producefatal cardiac arrhythmias of Torsades de Pointes (TdP). The ability toprolong the cardiac action potential duration was identified as beingdue to an action at the HERG potassium channel. For example, drugswithdrawn from the market due to QT prolongation, such as Cisapride andTerfenadine, are known to be potent HERG potassium channel blocker(Expert Opinion of Pharmacotherapy.; 2, pp. 947-973, 2000). Therefore,it would be desirable if there were provided a novel 5HT₄ selectiveagonist useful for the treatment of a variety of diseases such asgastroesophageal reflux disease, gastrointestinal disease, gastricmotility disorder, non-ulcer dyspepsia, functional dyspepsia, irritablebowel syndrome, constipation, dyspepsia, esophagitis, gastroesophageraldisease, nausea, central nervous system disease, alzheimers disease,cognitive disorder, emesis, migraine, neurological disease, pain, andcardiovascular disorders such as cardiac failure and heart arrhythmia,by systemic administration and with reduced inhibitory activity at HERGpotassium channel.

BRIEF DISCLOSURE OF THE INVENTION

[0010] It has now surprisingly been found that compounds broadly coveredby U.S. Application No. 60/343,371 are 5HT₄ selective agonists usefulfor the treatment of a variety of diseases such as gastroesophagealreflux disease, gastrointestinal disease, gastric motility disorder,non-ulcer dyspepsia, functional dyspepsia, irritable bowel syndrome,constipation, dyspepsia, esophagitis, gastroesophageral disease, nausea,central nervous system disease, alzheimers disease, cognitive disorder,emesis, migraine, neurological disease, pain, and cardiovasculardisorders such as cardiac failure and heart arrhythmia, by systemicadministration and with reduced inhibitory activity at HERG channel.Inhibitory activity at HERG channel was estimated from affinity for HERGtype potassium channel was investigated by checking [³H]dofetilidebinding, which can predict inhibitory activity at HERG channel (Eur. J.Pharmacol., 430, pp147-148, 2001). Selected compounds with low[³H]dofetilide binding activity were evaluated in I_(HERG) assay tocheck activity at HERG channel. Introducing a branched chain group tonitrogen atom in piperidine ring contributed to potent 5-HT₄ receptoragonist activities with reduced inhibitory activity at HERG channel. Thecompounds of the present invention may show less toxicity, goodabsorption, distribution and less drug-drug interaction, and havemetabolic stability.

[0011] The present invention provides a compound of the followingformula (I):

[0012] or a pharmaceutically acceptable salt thereof, wherein

[0013] R¹ represents a hydrogen atom or a halogen atom;

[0014] R²represents a methyl group or an ethyl group;

[0015] R³ represents a branched alkyl group having from 3 to 6 carbonatoms or an alkyl group having from 3 to 6 carbon atoms substituted byan alkoxy group having from 1 to 6 carbon atoms;

[0016] with the proviso that when the terminal carbon atom of said alkylgroup of R³ is substituted by said alkoxy group, said alkyl group is abranched alkyl group.

[0017] The imidazopyridine compounds of this invention have 5-HT₄receptor agonistic activities, and are thus useful for the treatment orprevention of disease conditions mediated by 5-HT₄ receptor activitieswith reduced inhibitory activity at HERG channel.

[0018] Thus, the present invention provides a pharmaceutical compositionfor the treatment of disease conditions mediated by 5-HT₄ receptoractivities, in a mammalian subject, which comprises administering tosaid subject a therapeutically effective amount of a compound of formula(I).

[0019] Further, the present invention also provides a pharmaceuticalcomposition for the treatment of gastroesophageal reflux disease,gastrointestinal disease, gastric motility disorder, upper gut motilitydisorder, non-ulcer dyspepsia, functional dyspepsia, irritable bowelsyndrome, constipation, dyspepsia, esophagitis, gastroesophageraldisease, nausea, central nervous system disease, alzheimers disease,cognitive disorder, emesis, migraine, neurological disease, pain,ischaemic stroke, anxiety, cardiovascular disorders such as cardiacfailure and heart arryhthmia, or the like, which comprises atherapeutically effective amount of the imidazopyridine compound offormula (I) or a pharmaceutically acceptable salt thereof together witha pharmaceutically acceptable carrier.

[0020] Also, the present invention provides a method for the treatmentof disease conditions mediated by 5-HT₄ receptor activities, in amammalian subject, which comprises administering to said subject atherapeutically effective amount of a compound of formula (I) or apharmaceutically acceptable salt thereof. Further, the present inventionprovides a method for the treatment of the disease conditions asmentioned above. Furthermore, the present invention provides use of thecompound of formula (I) or a pharmaceutically acceptable salt thereof inthe manufacture of a medicament for the treatment or prevention ofdisease conditions mediated by 5-HT₄ receptor activity, in a mammaliansubject. The conditions mediated by 5-HT₄ receptor activity are thosediseases or disorders described as above.

DETAILED DESCRIPTION OF THE INVENTION

[0021] As used herein, unless indicated otherwise, the article “a” or“an” refers to both the singular and plural form of the object to whichit refers.

[0022] As used herein, the term “halogen” means fluoro, chloro, bromoand iodo, preferably fluoro or chloro.

[0023] As used herein, the term “alkyl” means straight or branched chainsaturated radicals, including, but not limited to methyl, ethyl,n-propyl, isopropyl, n-butyl, iso-butyl, secondary-butyl,tertiary-butyl, iso-pentyl, neo-pentyl, tertiary-pentyl or iso-hexyl.

[0024] As used herein, the term “branched alkyl” means branched chainsaturated radicals, including, but not limited to isopropyl, iso-butyl,secondary-butyl, tertiary-butyl, iso-pentyl, neo-pentyl, tertiary-pentylor iso-hexyl.

[0025] As used herein, the term “alkoxy” means alkyl-O—, including, butnot limited to methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy,iso-butoxy, secondary-butoxy, tertiary-butoxy.

[0026] The term “treating”, as used herein, refers to reversing,alleviating, inhibiting the progress of, or preventing the disorder orcondition to which such term applies, or one or more symptoms of suchdisorder or condition. The term “treatment” as used herein refers to theact of treating, as “treating” is defined immediately above.

[0027] As used herein, the term “modulator” means compounds, agonists,antagonists, ligands, substrates and enzymes, which directly orindirectly affect regulation of the receptor activity.

[0028] In the compounds of formula (I), R¹ represents preferably, ahydrogen atom or a chlorine atom; more preferably a chlorine atom.

[0029] In the compounds of formula (I), R³ represents preferably aniso-butyl group, a tert-butylethyl group; and said alkyl group in R³ isunsubstituted or is substituted by a methoxy group.

[0030] Preferred individual compound of this invention is:

[0031]5-amino-N-[(1-isobutylpiperidin4-yl)methyl]-2-methylimidazo[1,2-a]pyridine-8-carboxamideor a salt thereof.

[0032] Preferred individual compound of this invention is:

[0033]5-amino-6-chloro-N-{[1-(3,3-dimethylbutyl)piperidin-4-yl]methyl}-2-ethylimidazo[1,2-a]pyridine-8-carboxamideor a salt thereof.

[0034] Preferred individual compound of this invention is:

[0035]5-amino-6-chloro-2-ethyl-N-{[1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methyl}imidazo[1,2-a]pyridine-8-carboxamideor a salt thereof.

[0036] Preferred individual compound of this invention is:

[0037]5-amino-6-chloro-2-methyl-N-{[1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methyl}imidazo[1,2-a]pyridine-8-carboxamideor a salt thereof.

[0038] Preferred individual compound of this invention is:

[0039]5-amino-6-chloro-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-a]pyridine-8-carboxamideor a salt thereof.

General Synthesis

[0040] The imidazopyridine compounds of formula (I) of this inventionmay be prepared by a variety of synthetic methods. Unless indicatedotherwise, all variables (e.g. R¹, R² and R³) are defined as set forthherein. For example, the imidazopyridine compounds of formula (I), maybe prepared by saponification of a carboxylate compound (II) to obtain acorresponding carboxylic acid compound (III), followed by a couplingreaction of the compound (III) with an amine compound (IV), as indicatedin the following Scheme 1.

[0041] wherein R′ is C₁₋₃ alkyl or benzyl.

[0042] In Scheme 1, the carboxylate compound (II) may be first subjectedto saponification of the ester residue at the 8-position of theimidazopyridine ring, followed by acidification to afford acorresponding carboxylic acid (III). Then, the compound (III) may becoupled with the amine compound (IV) to give an imidazopyridine compound(I).

[0043] The saponification and the acidification may be carried out byconventional procedures. In a typical procedure, the saponification iscarried out by treatment with sodium hydroxide or lithium hydroxide in asuitable reaction-inert solvent. Suitable solvents include, for example,alcohols such as methanol, ethanol, propanol, butanol, 2-methoxyethanol,and ethylene glycol; ethers such as tetrahydrofuran (THF),1,2-dimethoxyethane (DME), and 1,4-dioxane; halogenated hydrocarbonssuch as chloroform, dichloroethane, and 1,2-dichloroethane; amides suchas N,N-dimethylformamide (DMF) and hexamethylphospholictriamide; andsulfoxides such as dimethyl sulfoxide (DMSO). This reaction may becarried out at a temperature in the range from −20 to 100° C., usuallyfrom 20° C. to 65° C. for 30 minutes to 24 hours, usually 60 minutes to10 hour. In a typical procedure, the acidification is carried out bytreatment with diluted hydrochloric acid or 10% aqueous citric acid in asuitable reaction-inert solvent such as water at a temperature in therange from −20 to 65° C., usually from 0° C. to 30° C. for 30 minute to10 hour, usually 30 minutes to 2 hours.

[0044] The coupling reaction may be carried out in the presence of asuitable condensation agent in a reaction-inert solvent. Suitablecondensation agents include 1,1′-carbonyldiimidazole (CDI),diisopropylcarbodiimide (DIC), dicyclohexylcarbodiimide (DCC), watersoluble carbodiimide (WSC),2-ethoxy-N-ethoxycarbonyl-1,2-dihydroquinoline,benzotriazol-1-yloxy-tris(dimethylamino) phosphonium hexafluorophosphate(BOP), diethyl azodicarboxylate-triphenylphosphine,diethylcyanophosphonate (DEPC), diphenylphosphorylazide (DPPA),bromotripyrrolidino phosphonium hexafluorophosphate (PyBrop[trademark]),bis(2-oxo-3-oxazolidinyl) phosphinic chloride (BOPCl),benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium hexafluorophosphate(PyBOP), 2-(1-H-benzotriazole-1-yl)-1,1,3,3,-tetramethyluroniumhexafluorophosphate (HBTU) and ethyl chloroformate. Suitablereaction-inert solvents include aqueous or non-aqueous organic solventssuch as THF, DMF, 1,4-dioxane, acetone, DME and acetonitrile; andhalogenated hydrocarbons such as chloroform, dichloromethane and1,2-dichloroethane (preferably dichloromethane). This reaction may becarried out at a temperature in the range from −20 to 80° C., usuallyfrom 0° C. to 30° C. for 30 minutes to 100 hours, usually 5 hours to 24hours.

[0045] Scheme 2:

[0046] The carboxylate compounds (II) used as starting materials inScheme 1 may be prepared in the following reaction steps.

[0047] In Scheme 2, a nicotinate compound (V) wherein R′ is C₁₋₃ alkylor benzyl and Z is halogen; and the amino group is protected by apivaloyl group, may be reacted with an ammonia to obtain a compound(VIII). This reaction is generally carried out in a sealed tube. Thisreaction can be carried out in a suitable reaction-inert solvent such asmethanol, ethanol, propanol, butanol, 2-methoxyethanol and THF. Thisreaction may be carried out at a temperature in the range from 30 to150° C., usually from 50° C. to 100° C. for 30 minutes to 24 hours,usually 30 minutes to 12 hours. When R¹ is halo, the compound (VIII) istreated with halogen or N-halogenated succimide or SELECTFLUOR™(1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octaneditetrafluoroborate commercially available from Aldrich) underappropriate conditions, to obtain a compound (IX) wherein R¹ is halo.This reaction can be carried out in a suitable reaction-inert solventsuch as carboxylic acids (e.g., acetic acid, propionic acid and butylicacid); halogenated hydrocarbons such as chloroform, dichloroethane and1,2-dichloroethane; amides such as DMF and hexamethylphospholictriamide;sulfoxides such as DMSO; acetonitrile; benzene, toluene, xylene; andpyridine. This reaction may be carried out at a temperature in the rangefrom 0 to 80° C., usually from 25 to 70° C. for 5 minutes to 24 hours,usually 15 minutes to 8 hours. Then, the compound (IX) may be subject todeprotection of an amino-protecting group, to obtain a compound (X). Thedeprotection may be carried out in the presence of base (e.g., potassiumtert-butoxide, sodium ethoxide and sodium hydroxide) or acids (e.g.,hydrochloric acid and sulfuric acid). The deprotection can be carriedout in a suitable reaction-inert solvent such as methanol at atemperature in the range from 25 to 80° C., usually from 50 to 65° C.for 10 minutes to 24 hours, usually 30 minutes to 10 hours.

[0048] Then, the compound (X) may be reacted with a compound (XI)wherein X′ is halogen, to obtain a compound (II) and a compound (XII).This reaction can be carried out in the presence of 2-halogenatedaldehyde or 2-halogenated ketone (compound (XI)) in a suitablereaction-inert solvent such as methanol, ethanol, propanol and butanolat a temperature in the range from 25 to 120° C., usually from 50° C. to65° C. for 8 hours to 72 hours, usually 8 hours to 24 hours. Theresulting mixture of the compound (II) and the compound (XII) may besubjected to conventional separation techniques to obtain the compound(II). Suitable conventional separation techniques include silica gelcolumn chromatography.

[0049] In addition, starting compounds of formula (V) are known or maybe prepared from a known compound according to procedures known to thoseskilled in the art.

[0050] Scheme 3:

[0051] Compounds (I′) (Compound (I) wherein R¹ is hydrogen) can beprepared by subjecting a compound (I) wherein R¹ is halo, to catalytichydrogenation.

[0052] In Scheme 3, the catalytic hydrogenation can be carried out inthe presence of hydrogen or hydrogen source such as ammonium formate,triethylsilane and a suitable metal containing catalysts such aspalladium, platinum, nickel, platinum oxide and rhodium in a suitablereaction-inert solvent such as methanol. The preferred catalyst ispalladium on carbon. This hydrogenation can be carried out at atemperature in the range from 20 to 100° C., usually from 25° C. to 80°C. for 5 minutes to 48 hours, usually 30 minutes to 2 hours.

[0053] where R′, Z and X′ are each as set forth in Scheme 2.

[0054] In scheme 4, the compound (VI) may be reacted with an ammoniawater to obtain a compound (VII). This reaction is generally carried outin a sealed tube. This reaction can be carried out in a suitablereaction-inert solvent. Suitable solvents include, for example, alcoholssuch as methanol, ethanol, propanol, butanol, 2-methoxyethanol andethylene glycol; ethers such as THF, DME, diethyl ether, diisopropylether, diphenyl ether and 1,4-dioxane; halogenated hydrocarbons such aschloroform, dichloroethane and 1,2-dichloroethane; amides such as DMFand hexamethylphospholictriamide; sulfoxides such as DMSO; acetonitrile;benzene, toluene, xylene; and pyridine. This reaction may be carried outat a temperature in the range from 30 to 150° C., usually from 50° C. to100° C. for 30 minutes to 24 hours, usually 30 minutes to 12 hours.Compounds (II) may be prepared by reacting a compound (VII) with thecompound (XI) under appropriate conditions. This reaction can be carriedout in a suitable reaction-inert solvent such as methanol. This reactionmay be carried out at a temperature in the range from 25 to 65° C.,usually from 50° C. to 65° C. for 30 minutes to 48 hours, usually 30minutes to 12 hours.

[0055] Scheme 5:

[0056] The nicotinate compounds (V′) and (VI) used as starting materialsin Scheme 2, 4 and 6 may be prepared in the following reaction steps.

[0057] where R′ is as set forth in Scheme 2.

[0058] In scheme 5, a pyridine compound (XIII) wherein Z, each of whichcan be the same or different, is halogen, may be reacted with an ammoniawater to obtain a compound (XIV). This reaction is generally carried outin a sealed tube. This reaction may be carried out at a temperature inthe range from 50 to 200° C., usually from 100° C. to 160° C. for 30minutes to 24 hours, usually 30 minutes to 12 hours. The compound (XIV)is treated with acyl chloride, for example, pivaloyl chloride in thepresence of base, such as diisopropylethylamine, triethylamine, pyridineand lutidine to obtain a mixture of compound (XV). This reaction can becarried out in a suitable reaction-inert solvent. Suitable solventsinclude, for example, halogenated hydrocarbons such as chloroform,dichloroethane and 1,2-dichloroethane. This reaction may be carried outat a temperature in the range from −20 to 50° C., usually from −10° C.to 30° C. for 30 minutes to 24 hours, usually 30 minutes to 10 hours.The compound (XV) is treated with alkaline metal, for example, n-BuLifollowed by alkyl haloformate, for example, ethyl chloroformate orcarbobenzyloxychloride to obtain a compound (V′) and (VI). This reactioncan be carried out in a suitable reaction-inert solvent. Suitablesolvents include, for example, ethers such as THF, DME, diethyl ether,diisopropyl ether, diphenyl ether and 1,4-dioxane. This reaction may becarried out at a temperature in the range from −100 to 50° C., usuallyfrom −100 to 20° C. for 5 minutes to 24 hours, usually 15 minutes to 8hours. In addition, starting compounds of formula (XIII) are known ormay be prepared from a known compound according to procedures known tothose skilled in the art, for example, Helv. Chim. Acta (1976), 59,229-35, J. Chem. Soc., Perkin Trans.1 (1996), 519-24 and J. Chem. Soc.,Chem. Commun. (1988), 1482-3.

[0059] Scheme 6:

[0060] The carboxylate compounds (II) used as starting materials inScheme 1 may be prepared in the following reaction steps.

[0061] In Scheme 6, a nicotinate compound (V′) wherein R′ is C₁₋₃ alkylor bezyl and Z, each of which can be the same or different, is halogen;and the amino group is protected by a pivaloyl group, may be reactedwith an ammonia to obtain a compound (IX). This reaction is generallycarried out in a sealed tube. This reaction can be carried out in asuitable reaction-inert solvent such as methanol, ethanol, propanol,butanol, 2-methoxyethanol and tetrahydrofuran (THF). This reaction maybe carried out at a temperature in the range from 30 to 150° C., usuallyfrom 50° C. to 100° C. for 30 minutes to 24 hours, usually 30 minutes to12 hours. Then, the compound (IX) may be subject to deprotection of anamino-protecting group, to obtain a compound (X). The deprotection maybe carried out in the presence of base (e.g., potassium tert-butoxide,sodium ethoxide and sodium hydroxide) or acids (e.g., hydrochloric acidand sulfuric acid). The deprotection can be carried out in a suitablereaction-inert solvent such as methanol at a temperature in the rangefrom 25 to 80° C., usually from 50 to 65° C. for 10 minutes to 24 hours,usually 30 minutes to 10 hours.

[0062] Then, the compound (X) may be reacted with a compound (XI) whereX′ is halogen to obtain a compound (II) and a compound (XII). Thisreaction can be carried out in the presence of 2-halogenated aldehyde or2-halogenated ketone (compound (XI)) in a suitable reaction-inertsolvent such as methanol, ethanol, propanol and butanol at a temperaturein the range from 25 to 120° C., usually from 50° C. to 65° C. for 8hours to 72 hours, usually 8 hours to 24 hours. The resulting mixture ofthe compound (II) and the compound (XII) may be subjected toconventional separation techniques to obtain the compound (II). Suitableconventional separation techniques include silica gel columnchromatography.

[0063] wherein R′ is C₁₋₃ alkyl, Z is halogen, and PG is a protectinggroup.

[0064] In Scheme 7, the carboxylic acid compound (III) may be coupledwith the amine compound (XVI) to give an imidazopyridine compound(XVII). Then, the compound (XVII) may be subjected to deprotection ofthe protecting group of nitrogen atom in the piperidine ring, followedby alkylation to afford an imidazopyridine compound (I′).

[0065] The coupling reaction may be carried out in the presence of asuitable condensation agent in a reaction-inert solvent. Suitablecondensation agents include 1,1′-carbonyldiimidazole (CDI),diisopropylcarbodiimide (DIC), dicyclohexylcarbodiimide (DCC), watersoluble carbodiimide (WSC),2-ethoxy-N-ethoxycarbonyl-1,2-dihydroquinoline,benzotriazol-1-yloxy-tris(dimethylamino) phosphonium hexafluorophosphate(BOP), diethyl azodicarboxylate-triphenylphosphine,diethylcyanophosphonate (DEPC), diphenylphosphorylazide (DPPA),bromotripyrrolidino phosphonium hexafluorophosphate (PyBrop[trademark]),bis(2-oxo-3-oxazolidinyl) phosphinic chloride (BOPCl),benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium hexafluorophosphate(PyBOP), 2-(1-H-benzotriazole-1-yl)-1,1,3,3,-tetramethyluroniumhexafluorophosphate (HBTU) and ethyl chloroformate. Suitablereaction-inert solvents include aqueous or non-aqueous organic solventssuch as THF, DMF, 1,4-dioxane, acetone, DME and acetonitrile; andhalogenated hydrocarbons such as chloroform, dichloromethane and1,2-dichloroethane (preferably dichloromethane). This reaction may becarried out at a temperature in the range from −20 to 80° C., usuallyfrom 0° C. to 30° C. for 30 minutes to 100 hours, usually 5 hours to 24hours.

[0066] The obtained amino compound may be subjected to deprotection ofan amino-protecting group, to obtain a compound (XVIII). Thedeprotection may be carried out by a number of standard procedures knownto those skilled in the art (e.g., “Protection for the Hydroxy Group andthe Amino Group ”, in Protective Groups in Organic Synthesis, 2ndEdition, T. W. Greene and P. G. M. Wuts, Ed., John Wiley and Sons, Inc.1991, pp. 10-142, 309-405). Then, alkylation of amino group inpiperidine ring may be carried out under the conventional conditions.The compound may be treated with appropriate alkyl halides (R⁶-Z) in thepresence of a base such as diisopropylethylamine, triethylamine,pyridine, lutidine, potassium carbonate, sodium bicarbonate, sodiumcarbonate or the like, in a reaction inert solvent such asdichrolomethane, THF or DMF at about 0° C. to about 100° C. for about 5minutes to about 48 hours.

[0067] Scheme 8:

[0068] An amino compound (XXIII) wherein R^(a) and R^(b) are C₁₋₄ alkyland RC is C₁₋₆ alkyl, may be prepared in the following reaction steps.

[0069] where Z is halogen, PG is a protecting group and Y is methylene.

[0070] In scheme 8, piperidine compound (XIX) may be reacted with anepoxide compound (XX) to obtain a hydroxy compound (XXI). This reactioncan be carried out in a suitable reaction-inert solvent such as THF,DMF, acetonitrile, dichloromethane, 1,2-dichloroethane, DMSO,methylethylketone, methanol, ethanol, propanol, butanol, iso-butanol,sec-butanol and tert-butanol at a temperature in the range from −50 to250° C., usually from 0° C. to 200° C. for 30 minutes to 100 hours,usually 1 hour to 80 hours. This reaction may be carried out in thepresence of a metal halide such as sodium iodide, potassium iodide andlithium iodide. The conversion of hydroxy compound (XXI) to an alkoxycompound (XXII) may be carried out under the conventional method. Thealkylation of a hydroxy group may be carried out under the conventionalconditions. The compound may be treated with appropriate alkyl halides(R⁶-Z) in the presence of a base such as sodium methoxide, sodiumethoxide, potassium tert-butoxide, sodium hydride or potassium hydride,or the like, in a reaction inert solvent such as diethyl ether, DME,DMSO, THF or DMF at about 0° C. to about 200° C., usually from 0° C. to200° C., for about 5 minutes to about 100 hours, usually 1 hour to 80hours. Alternatively, hydroxy compound (XXI) may be treated with R^(c)₃O⁺BF₄ ⁻ to provide the compound (XXII). This reaction can be carriedout in a suitable reaction-inert solvent such as 1,2-dichloromethane,dichloroethane, benzene, toluene and nitromethane at a temperature inthe range from −50 to 200° C., usually from 0° C. to 100° C. for 30minutes to 100 hours, usually 1 hour to 80 hours. The obtained compound(XXII) may be subjected to deprotection of an amino-protecting group, toobtain a compound (XXIII). The deprotection may be carried out by anumber of standard procedures known to those skilled in the art (e.g.,“Protection for the Hydroxy Group and the Amino Group ”, in ProtectiveGroups in Organic Synthesis, 2nd Edition, T. W. Greene and P. G. M.Wuts, Ed., John Wiley and Sons, Inc. 1991, pp. 10-142, 309-405).

[0071] The nicotinate compounds (X) may be prepared in the followingreaction steps.

[0072] In scheme 9, a pyridine compound (XXIV) may be treated withn-BuLi followed by R′COZ or R′COR′ wherein R′ is C₁₋₃ alkyl or benzyland Z is halogen, to obtain a compound (XXVI). This reaction can becarried out in a suitable reaction-inert solvent. Suitable solventsinclude, for example, ethers such as THF, DME, diethyl ether,diisopropyl ether, diphenyl ether and 1,4-dioxane. This reaction may becarried out at a temperature in the range from −100 to 50° C., usuallyfrom −100 to 20° C. for 5 minutes to 24 hours, usually 15 minutes to 8hours. Alternatively, the compound (XXVI) may be prepared from thepyridine compound (XXIV) by carboxylation followed by esterification.The pyridine compound (XXIV) may be treated with n-BuLi followed bycarbon dioxide (gas or dry ice) to obtain a carboxylic acid compound(XXV). This reaction can be carried out in a suitable reaction-inertsolvent. Suitable solvents include, for example, ethers such as THF,DME, diethyl ether, diisopropyl ether, diphenyl ether and 1,4-dioxane.This reaction may be carried out at a temperature in the range from −100to 50° C., usually from −100 to 20° C. for 5 minutes to 24 hours,usually 15 minutes to 8 hours. The compound (XXV) may be subjected toesterification to obtain the compound (XXVI). The esterification may becarried out by a number of standard procedures known to those skilled inthe art (e.g., Protective Groups in Organic Synthesis, Third edition.ed. T. W. Green and P. G. M. Wuts, Wiley-Interscience., pp 373-377.).Typical esterification can be carried out with a suitable C₁₋₃alkylhalide or benzylhalide in the presence of a base in a suitablereaction-inert solvent. Suitable solvents include, for example, etherssuch as THF, DME, diethyl ether, diisopropyl ether, diphenyl ether, DMF,DMSO, R′OH and 1,4-dioxane. Suitable bases include, for example, K₂CO₃,Cs₂CO3, NaHCO₃ and DBU. This reaction may be carried out at atemperature in the range from −100 to 200° C., usually from −10 to 100°C. for 1 to 72 hours, usually 2 to 60 hours. The esterification alsocarried out with trimethylsilyldiazomethane in a suitable reaction-inertsolvent. Suitable solvents include, for example, methanol, benzene andtoluene. This reaction may be carried out at a temperature in the rangefrom −100 to 200° C., usually from −10 to 100° C. for 1 minute to 72hours, usually 0.5 to 60 hours. The esterification also carried out withdiazomethane in a suitable reaction-inert solvent. Suitable solventsinclude, for example, diethyl ether. This reaction may be carried out ata temperature in the range from −100 to 200° C., usually from −50 to100° C. for 1 minute to 72 hours, usually 0.5 to 60 hours.Alternatively, the esterification may be carried out with R′OH, in thepresence of a coupling agent and a tertiaryamine in a suitable solvent.Suitable coupling agents include, for example, DCC, WSC,diisoproopylcyanophosphonate (DIPC), BOPCl and 2,4,6-trichlorobenzoicacid chloride. Suitable tertiaryamines include, for example,diisopropylethylamine, triethylamine. Suitable solvents include, forexample, DMF, THF, diethyl ether, DME, dichloromethane and1,2-dichloroethane. This reaction may be carried out at a temperature inthe range from −100 to 200° C., usually from −50 to 100° C. for 1 minuteto 100 hours, usually 0.5 to 80 hours. When R¹ is halo, the compound(XXVI) can be treated with halogen or N-halogenated succimide orSELECTFLUOR™ (1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octaneditetrafluoroborate commercially available from Aldrich) underappropriate conditions, to obtain a compound (XXVII) wherein R¹ is halo.This reaction can be carried out in a suitable reaction-inert solventsuch as carboxylic acids (e.g., acetic acid, propionic acid and butylicacid); halogenated hydrocarbons such as chloroform, dichloroethane and1,2-dichloroethane; amides such as DMF and hexamethylphospholictriamide;sulfoxides such as DMSO; acetonitrile; benzene, toluene, xylene; andpyridine. This reaction may be carried out at a temperature in the rangefrom 0 to 80° C., usually from 25 to 70° C. for 5 minutes to 24 hours,usually 15 minutes to 8 hours. Then, the compound (XXVII) may be subjectto deprotection of an amino-protecting group, to obtain a compound (X).The deprotection may be carried out in the presence of base (e.g.,potassium tert-butoxide, sodium ethoxide and sodium hydroxide) or acids(e.g., hydrochloric acid and sulfuric acid). The deprotection can becarried out in a suitable reaction-inert solvent such as methanol at atemperature in the range from 25 to 80° C., usually from 50 to 65° C.for 10 minutes to 24 hours, usually 30 minutes to 10 hours.

[0073] In addition, starting compound of formula (XXIV) is known or maybe prepared from a known compound according to procedures known to thoseskilled in the art, for example, J. Am. Chem. Soc. (1986), 108(12),3310-18.

[0074] The present invention includes salt forms of the compounds (I) asobtained above. Insofar as the imidazopyridine compounds of thisinvention are basic compounds, they are capable of forming a widevariety of different salts with various inorganic or organic acids.

[0075] The acids which are used to prepare the pharmaceuticallyacceptable acid addition salts of the aforementioned imidazopyridinebase compounds of formula (I) are those which form non-toxic acidaddition salts, i.e., salts containing pharmaceutically acceptableanions, such as the chloride, bromide, iodide, nitrate, sulfate orbisulfate, phosphate or acid phosphate, acetate, lactate, citrate oracid citrate, tartrate or bi-tartrate, succinate, malate, fumarate,gluconate, saccharate, benzoate, methanesulfonate, ethanesulfonate,benzenesulfonate, p-toluenesulfonate and pamoate (i.e.,1.1′-methylene-bis-(2-hydroxy-3-naphthoate). The acid addition salts canbe prepared by conventional procedures.

[0076] The compounds of formula (I) of this invention may contain one ormore asymmetric centers. Thus, the compounds can exist in separated (+)-and (−)-optically active forms, as well as in the racemic form thereof.The present invention includes all such forms within its scope.Individual isomers can be obtained by known methods, such as opticallyselective reaction or chromatographic separation in the preparation ofthe final product or its intermediate.

[0077] In addition, when the compounds of this invention form hydratesor solvates they are also within the scope of this invention.

[0078] The imidazopyridine compounds of this invention have 5-HT₄receptor binding activity (e.g., agonist or antagonist activities), andthus are useful for the treatment or prevention of gastroesophagealreflux disease, gastrointestinal disease, gastric motility disorder,upper gut motility disorder, non-ulcer dyspepsia, functional dyspepsia,irritable bowel syndrome, constipation, dyspepsia, esophagitis,gastroesophageral disease, nausea, central nervous system disease,alzheimers disease, cognitive disorder, emesis, migraine, neurologicaldisease, pain, ischaemic stroke, anxiety, cardiovascular disorders suchas cardiac failure and heart arryhthmia, or the like in mammalian,especially human.

[0079] The compounds of the invention may advantageously be employed incombination with one or more other therapeutic ingredients selected froman antibiotic, anti-fungal and anti-viral agent.

Method for Assessing Biological Activities

[0080] The 5-HT₄ receptor binding affinities of the compounds of thisinvention are determined by the following procedures.

[0081] Membrane Preparation

[0082] Pig heads were supplied from an abattoir. Striatal tissues weredissected, weighed and homogenized in 15 volumes of 50 mM ice-cold HEPES(pH 7.5) in a Polytron homogenizer (30 sec at full speed). Suspensionwas centrifuged at 48,000 g and 4° C. for 15 min. The resulting pelletwas resuspended in an appropriate volume of 50 mM ice-cold HEPES,dispensed into aliquots and stored at −80° C. until use.

[0083] Bovine heads were also supplied from an abattoir. Striataltissues were dissected, weighed and homogenized in 20 volumes of 50 mMice-cold Tris-HCl (pH 7.4) in a Polytron homogenizer (30 sec at fullspeed). Suspension was centrifuged at 20,000 g and 4° C. for 30 min. Theresulting pellet was resuspended in 15 volumes of 50 mM ice-coldTris-HCl, homogenized and centrifuged again in the same way. The finalpellet was resuspended in an appropriate volume of 50 mM Tris-HCl,dispensed into aliquots and stored at −80° C. until use.

[0084] Cerebral cortical tissues were removed from male Sprague-Dawley(SD) rats (Japan SLC), weighed and placed in 10 volumes of 50 mMice-cold Tris-HCl (pH 7.5). This was homogenized in a Polytronhomogenizer (30 sec at full speed) and subsequently centrifuged at48,000 g and 4° C. for 15 min. The resulting pellet was resuspended in50 mM ice-cold Tris-HCl, homegenized and centrifuged again in the sameway. The final pellet was resuspended in an appropriate volume of 50 mMTris-HCl, dispensed into aliquots and stored at −80° C. until use.

[0085] The protein concentrations of homogenates were determined byBradford method or BCA protein method (Pierce) with BSA as a standard.

[0086] Binding Assays

[0087] Affinity of compounds for pig or bovine 5-HT4 and rat 5-HT3receptors were assessed with using radiolabeled specific ligands, GR113808({1-[2-(methylsulfonyl)ethyl]-4-piperidinyl}[methyl-³H]-1H-indole-3-carboxylate)and BRL 43694(1-Methyl-N-(9-[methyl-³H]-9-azabicyclo[3.3.1]non-3-yl)-1H-indazole-3-caboxamide).Compounds were incubated with 25-100 pM of [³H]-GR 113808 (Amersham) and0.6-1 mg protein of pig or bovine striatal membranes suspended in afinal volume of 0.8-1 ml of 50 mM Tris-HCl (pH 7.5). Nonspecific bindingwas determined with 10-50 μM 5-HT. The binding of 0.3 nM [³H]-BRL 43694(NEN) was measured using 400 μg protein of rat cortical membranessuspended in a final volume of 500 μl of 50 mM Tris-HCl (pH 7.5).Nonspecific binding was determined with 10 μM 5-HT.

[0088] The plates were incubated at room temperature on a plate shakerfor 30 min. The assays were stopped by rapid filtration using a Brandellcell harvester through Wallac-B filters pre-soaked in 0.2%poly(ethylenimine) at 4° C. for 60-90min. The filters were washed threetimes with 1 ml of ice-cold 50 mM HEPES, and were dried in a microwaveor at room temperature. They were bagged and heated with meltilexscintillant (Wallac) or soaked in BetaplateScint (Wallac).Receptor-bound radioactivity was quantified using Big-spot counter,Betaplate counter (Wallac) or LS counter (Packard).

[0089] Human 5-HT4 Binding

[0090] Human 5-HT_(4(d)) transfected HEK293 cells were prepared andgrown in-house. The collected cells were suspended in 50 mM HEPES (pH7.4 at 4° C.) supplemented with protease inhibitor cocktail (Boehringer,1:1000 dilution) and homogenized using a hand held Polytron PT 1200disruptor set at full power for 30 sec on ice. The homogenates werecentrifuged at 40,000×g at 4° C. for 30 min. The pellets were thenresuspended in 50 mM HEPES (pH 7.4 at 4° C.) and centrifuged once morein the same manner. The final pellets were resuspended in an appropriatevolume of 50 mM HEPES (pH 7.4 at 25° C.), homogenized, aliquoted andstored at −80° C. until use. An aliquot of membrane fractions was usedfor protein concentration determination using BCA protein assay kit(PIERCE) and ARVOsx plate reader (Wallac).

[0091] For the binding experiments, 25 μl of test compounds wereincubated with 25 μl of [³H]-GR113808 (Amersham, final 0.2 nM) and 150μl of membrane homogenate and WGA-SPA beads (Amersham) suspensionsolutions (10 μg protein and 1 mg SPA beads/well) for 60 minutes at roomtemperature. Nonspecific binding was determined by 1 μM GR113808(Tocris) at the final concentration. Incubation was terminated bycentrifugation at 1000 rpm. Receptor-bound radioactivity was quantifiedby counting with MicroBeta plate counter (Wallac).

[0092] Functional Assay:

[0093] The presence of 5-HT₄ receptors in the rat oesophagus and theability to demonstrate partial agonism in the TMM preparation arereported in the literature (See G. S. Baxter et al.Naunyn-Schmiedeberg's Arch Pharmacol (1991) 343: 439-446; M. Yukiko etal. JPET (1997) 283:1000-1008; and J. J. Reeves et al. Br. J. Pharmacol.(1991) 103: 1067-1072). More specifically, partial agonist activity canbe measured according to the following procedures.

[0094] Male SD rats (Charles River) weighing 250-350 g were stunned andthen killed by cervical dislocation. The oesophagus was dissected fromimmediately proximal to the stomach (including piece of stomach to markdistal end) up to the level of the trachea and then placed in freshKrebs' solution.

[0095] The outer skeletal muscle layer was removed in one go by peelingit away from the underlying smooth muscle layer using forceps (stomachto tracheal direction). The remaining inner tube of smooth muscle wasknown as the TMM. This was trimmed to 2 cm from the original‘stomach-end’ and the rest discarded.

[0096] The TMMs were mounted as whole ‘open’ tubes in longitudinalorientation in 5 ml organ baths filled with warm (32° C.) aerated Krebs.Tissues were placed under an initial tension of 750 mg and allowed toequilibrate for 60 minutes. The tissues were re-tensioned twice at 15minute intervals during the equilibration period. The pump flow rate wasset to 2 ml/min during this time.

[0097] Following equilibration, the pump was switched off. The tissueswere exposed to 1 μM carbachol and contracted and reached a steadycontractile plateau within 15 minutes. Tissues were then subject to 1 μM5-HT (this was to prime the tissues). The tissues relaxed in response to5-HT fairly rapidly—within 1 minute. As soon as maximal relaxation hasoccurred and a measurement taken, the tissues were washed at maximumrate (66 ml/min) for at least 1 minute and until the original baseline(pre-carbachol and 5-HT) has returned (usually, the baseline drops belowthe original one following initial equilibration). The pump flow ratewas reduced to 2 ml/min and the tissues left for 60 minutes.

[0098] A cumulative concentration-effect-curve (CEC) to 5-HT wasconstructed across the range 0.1 nM to 1 μM, in half-log unit increments(5-HT curve 1 for data analysis). Contact time between doses was 3minutes or until plateau established. Tissues responded quicker asconcentration of 5-HT in the bath increases. At the end of the curve,the tissues were washed (at maximum rate) as soon as possible to avoiddesensitisation of receptors. Pump rate was reduced to 2 ml/min and thetissues left for 60 minutes.

[0099] A second CEC was carried out—either to 5-HT (for time controltissues), another 5-HT₄ agonist (standard) or a test compound (curve 2for data analysis). Contact time varied for other 5-HT₄ agonists andtest compounds and was tailored according to the tissues' individualresponses to each particular agent. In tissues exposed to a testcompound, a high concentration (1 μM) of a 5-HT₄ antagonist (SB 203,186:1H-Indole-3-carboxylic acid, 2-(1-piperidinyl)ethyl ester, Tocris) wasadded to the bath following the last concentration of test compound.This was to see if any agonist-induced relaxation (if present) could bereversed. SB 203,186 reversed 5-HT induced relaxation, restoring thetissue's original degree of carbachol-induced tone.

[0100] Agonist activity of test compounds was confirmed bypre-incubating tissues with 100nM standard 5HT₄ antagonist such as SB203,186. SB 203,186 was added to the bath 5 minutes before the additionof carbachol prior to curve 2. Tissues must be ‘paired’ for dataanalysis i.e. the test compound in the absence of SB 203,186 in onetissue was compared with the test compound in the presence of SB 203,186in a separate tissue. It was not possible to carry out a curve 3 i.e.5-HT curve 1, followed by the test compound curve 2 (−SB 203,186),followed by the test compound curve 3 (+SB 203,186).

[0101] Agonist-Induced cAMP Elevation in Human 5-HT_(4(d)) TransfectedHEK293 Cells

[0102] Human 5-HT_(4(d)) transfected HEK293 cells were establishedin-house. The cells were grown at 37° C. and 5% CO₂ in DMEM supplementedwith 10% FCS, 20 mM HEPES (pH 7.4), 200 μg/ml hygromycin B (Gibco), 100units/ml penicillin and 100 μg/ml streptomycin.

[0103] The cells were grown to 60-80% confluence. On the previous daybefore treatment with compounds dialyzed FCS (Gibco) was substituted fornormal and the cells were incubated overnight.

[0104] Compounds were prepared in 96-well plates (12.5 μl/well). Thecells were harvested with PBS/1 mM EDTA, centrifuged and washed withPBS. At the beginning of the assay, cell pellet was resuspended in DMEMsupplemented with 20 mM HEPES, 10 μM pargyline (Sigma) and 1 mM3-isobutyl-1-methylxanthine (Sigma) at the concentration of 1.6×10⁵cells/ml and left for 15 minutes at room temperature. The reaction wasinitiated by addition of the cells into plates (12.5 μl/well). Afterincubation for 15 minutes at room temperature, 1% Triton X-100 was addedto stop the reaction (25 μl/well) and the plates were left for 30minutes at room temperature. Homogenous time-resolved fluorescence-basedcAMP (Schering) detection was made according to the manufacturer'sinstruction. ARVOsx multilabel counter (Wallac) was used to measure HTRF(excitation 320 nm, emission 665 nm/620 nm, delay time 50 μs, windowtime 400 μs).

[0105] Data was analyzed based on the ratio of fluorescence intensity ofeach well at 620 nm and 665 nm followed by cAMP quantification usingcAMP standard curve. Enhancement of cAMP production elicited by eachcompound was normalized to the amount of cAMP produced by 1000 nMserotonin (Sigma).

[0106] Human Dofetilide Binding

[0107] Human HERG transfected HEK293S cells were prepared and grownin-house. The collected cells were suspended in 50 mM Tris-HCl (pH 7.4at 4° C.) and homogenized using a hand held Polytron PT 1200 disruptorset at full power for 20 sec on ice. The homogenates were centrifuged at48,000×g at 4° C. for 20 min. The pellets were then resuspended,homogenized, and centrifuged once more in the same manner. The finalpellets were resuspended in an appropriate volume of 50 mM Tris-HCl, 10mM KCl, 1 mM MgCl₂ (pH 7.4 at 4° C.), homogenized, aliquoted and storedat −80° C. until use. An aliquot of membrane fractions was used forprotein concentration determination using BCA protein assay kit (PIERCE)and ARVOsx plate reader (Wallac).

[0108] Binding assays were conducted in a total volume of 200 μl in96-well plates. Twenty μl of test compounds were incubated with 20 μl of[³H]-dofetilide (Amersham, final 5 nM) and 160 μl of membrane homogenate(25 μg protein) for 60 minutes at room temperature. Nonspecific bindingwas determined by 10 μM dofetilide at the final concentration.Incubation was terminated by rapid vacuum filtration over 0.5% presoakedGF/B Betaplate filter using Skatron cell harvester with 50 mM Tris-HCl,10 mM KCl, 1 mM MgCl₂, pH 7.4 at 4° C. The filters were dried, put intosample bags and filled with Betaplate Scint. Radioactivity bound tofilter was counted with Wallac Betaplate counter.

[0109] I_(HERG) Assay

[0110] HEK 293 cells which stably express the HERG potassium channelwere used for electrophysiological study. The methodology for stabletransfection of this channel in HEK cells can be found elsewhere (Z.Zhou et al., 1998, Biophysical journal, 74, pp230-241). Before the dayof experimentation, the cells were harvested from culture flasks andplated onto glass coverslips in a standard MEM medium with 10% FCS. Theplated cells were stored in an incubator at 37° C. maintained in anatmosphere of 95% O₂/5% CO₂. Cells were studied between 15-28 hrs afterharvest.

[0111] HERG currents were studied using standard patch clamp techniquesin the whole-cell mode. During the experiment the cells were superfusedwith a standard external solution of the following composition (mM);NaCl, 130; KCl, 4; CaCl₂, 2; MgCl₂, 1; Glucose, 10; HEPES, 5; pH 7.4with NaOH. Whole-cell recordings was made using a patch clamp amplifierand patch pipettes which have a resistance of 1-3 MOhm when filled withthe standard internal solution of the following composition (mM); KCl,130; MgATP, 5; MgCl₂, 1.0; HEPES, 10; EGTA 5, pH 7.2 with KOH. Onlythose cells with access resistances below 15MΩ and seal resistances >1GΩwas accepted for further experimentation. Series resistance compensationwas applied up to a maximum of 80%. No leak subtraction was done.However, acceptable access resistance depended on the size of therecorded currents and the level of series resistance compensation thatcan safely be used. Following the achievement of whole cellconfiguration and sufficient for cell dialysis with pipette solution (>5min), a standard voltage protocol was applied to the cell to evokemembrane currents. The voltage protocol is as follows. The membrane wasdepolarized from a holding potential of −80 mV to +20 mV for 1000 ms.This was followed by a descending voltage ramp (rate 0.5 mV msec⁻¹) backto the holding potential. The voltage protocol was applied to a cellcontinuously throughout the experiment every 4 seconds (0.25 Hz). Theamplitude of the peak current elicited around −40mV during the ramp wasmeasured. Once stable evoked current responses were obtained in theexternal solution, vehicle (0.5% DMSO in the standard external solution)was applied for 10-20 min by a peristalic pump. Provided there wereminimal changes in the amplitude of the evoked current response in thevehicle control condition, the test compound of either 0.3, 1,3, 10 μMwas applied for a 10 min period. The 10 min period included the timewhich supplying solution was passing through the tube from solutionreservoir to the recording chamber via the pump. Exposing time of cellsto the compound solution was more than 5 min after the drugconcentration in the chamber well reached the attempting concentration.There reversibility. Finally, the cells was exposed to high dose ofdofetilide (5 μM), a specific IKr blocker, to evaluate the insensitiveendogenous current.

[0112] All experiments were performed at room temperature (23±1° C.).Evoked membrane currents were recorded on-line on a computer, filteredat 500-1 KHz (Bessel—3dB) and sampled at 1-2KHz using the patch clampamplifier and a specific data analyzing software. Peak currentamplitude, which occurred at around −40 mV, was measured off line on thecomputer.

[0113] The arithmetic mean of the ten values of amplitude was calculatedunder control conditions and in the presence of drug. Percent decreaseof I_(N) in each experiment was obtained by the normalized current valueusing the following formula: I_(N)=(1−I_(D)/I_(C))×100, where I_(D) isthe mean current value in the presence of drug and I_(C) is the meancurrent value under control conditions. Separate experiments wereperformed for each drug concentration or time-matched control, andarithmetic mean in each experiment is defined as the result of thestudy. Test result is summarized as follows: 5HT4 Binding Dofetilide TIKi Binding Ki (Defetilide/ Chemical Structure [nM] [μM] 5HT4)

1.2 2.3 1,900 Compound A

4.6 6.0 1,300 Compound B

0.82 5.75 7,000 Compound of Example 1 of this invention

3.1 24.1 7,800 Compound of Example 2 of this invention

0.77 3.87 5,000 Compound of Example 3 of this invention

1.2 22.3 19,000 Compound of Example 4 of this invention

2.0 >24.0 >12,000 Compound of Example 5 of this invention

[0114] The compounds of Example 1-5 showed a TI value in the range of5,000-19,000, whereas a structurally similar comparative compound A andB showed TI values of 1,900 and 1,300.

[0115] The imidazopyridine compounds of this invention can beadministered via either the oral, parenteral or topical routes tomammals. In general, these compounds are most desirably administered tohumans in doses ranging from about 0.3 mg to about 750 mg per day,preferably from about 10 mg to about 500 mg per day, although variationswill necessarily occur depending upon the weight and condition of thesubject being treated, the disease state being treated and theparticular route of administration chosen. However, for example, adosage level that is in the range of from about 0.06 mg to about 2 mgper kg of body weight per day is most desirably employed for treatmentof inflammation.

[0116] The compounds of the present invention may be administered aloneor in combination with pharmaceutically acceptable carriers or diluentsby either of the above routes previously indicated, and suchadministration can be carried out in single or multiple doses. Moreparticularly, the novel therapeutic agents of the invention can beadministered in a wide variety of different dosage forms, i.e., they maybe combined with various pharmaceutically acceptable inert carriers inthe form of tablets, capsules, lozenges, troches, hard candies, powders,sprays, creams, salves, suppositories, jellies, gels, pastes, lotions,ointments, aqueous suspensions, injectable solutions, elixirs, syrups,and the like. Such carriers include solid diluents or fillers, sterileaqueous media and various nontoxic organic solvents, etc. Moreover,oralpharmaceutical compositions can be suitably sweetened and/orflavored. In general, the therapeutically-effective compounds of thisinvention are present in such dosage forms at concentration levelsranging from about 5% to about 70% by weight, preferably about 10% toabout 50% by weight.

[0117] For oral administration, tablets containing various excipientssuch as microcrystalline cellulose, sodium citrate, calcium carbonate,dipotassium phosphate and glycine may be employed along with variousdisintegrants such as starch and preferably corn, potato or tapiocastarch, alginic acid and certain complex silicates, together withgranulation binders like polyvinylpyrrolidone, sucrose, gelatin andacacia. Additionally, lubricating agents such as magnesium stearate,sodium lauryl sulfate and talc are often very useful for tablettingpurposes. Solid compositions of a similar type may also be employed asfillers in gelatin capsules; preferred materials in this connection alsoinclude lactose or milk sugar as well as high molecular weightpolyethylene glycols. When aqueous suspensions and/or elixirs aredesired for oral administration, the active ingredient may be combinedwith various sweetening or flavoring agents, coloring matter or dyes,and, if so desired, emulsifying and/or suspending agents as well,together with such diluents as water, ethanol, propylene glycol,glycerin and various like combinations thereof.

[0118] For parenteral administration, solutions of a compound of thepresent invention in either sesame or peanut oil or in aqueous propyleneglycol may be employed. The aqueous solutions should be suitablybuffered (preferably pH>8) if necessary and the liquid diluent firstrendered isotonic. These aqueous solutions are suitable for intravenousinjection purposes. The oily solutions are suitable for intra-articular,intra-muscular and subcutaneous injection purposes. The preparation ofall these solutions under sterile conditions is readily accomplished bystandard pharmaceutical techniques well known to those skilled in theart. Additionally, it is also possible to administer the compounds ofthe present invention topically when treating inflammatory conditions ofthe skin and this may preferably be done by way of creams, jellies,gels, pastes, ointments and the like, in accordance with standardpharmaceutical practice.

EXAMPLES

[0119] The invention is illustrated in the following non-limitingexamples in which, unless stated otherwise: all operations were carriedout at room or ambient temperature, that is, in the range of about18-25° C.; evaporation of solvent was carried out using a rotaryevaporator under reduced pressure with a bath temperature of up to about60° C.; reactions were monitored by thin layer chromatography (tlc) andreaction times are given for illustration only; melting points (m.p.)given are uncorrected (polymorphism may result in different meltingpoints); the structure and purity of all isolated compounds were assuredby at least one of the following techniques: tlc (Merck silica gel 60F₂₅₄ precoated TLC plates or Merck NH₂ F_(254s) precoated HPTLC plates),mass spectrometry, nuclear magnetic resonance (NMR), infrared redabsorption spectra (IR) or microanalysis. Yields are given forillustrative purposes only. Flash column chromatography was carried outusing Merck silica gel 60 (230-400 mesh ASTM) or Fuji SilysiaChromatorex® DU3050 (Amino Type, 30˜50 μm). Low-resolution mass spectraldata (EI) were obtained on a Automass 120 (JEOL) mass spectrometer.Low-resolution mass spectral data (ESI) were obtained on a Quattro II(Micromass) mass spectrometer. NMR data was determined at 270 MHz (JEOLJNM-LA 270 spectrometer) or 300 MHz (JEOL JNM-LA300) using deuteratedchloroform (99.8% D) or dimethylsulfoxide (99.9% D) as solvent unlessindicated otherwise, relative to tetramethylsilane (TMS) as internalstandard in parts per million (ppm); conventional abbreviations usedare: s=singlet, d=doublet, t=triplet, q=quartet, m=multiplet, br.=broad,etc. IR spectra were measured by a Shimazu infrared spectrometer(IR-470). Optical rotations were measured using a JASCO DIP-370 DigitalPolarimeter (Japan Spectroscopic CO, Ltd.). Chemical symbols have theirusual meanings; b.p. (boiling point), m.p. (melting point), l(liter(s)), ml (milliliter(s)), g (gram(s)), mg (milligram(s)), mol(moles), mmol (millimoles), eq. (equivalent(s)).

Example 15-AMINO-6-CHLORO-N-[(1-ISOBUTYLPIPERIDIN-4-YL)METHYL]-2-METHYLIMIDAZO[1,2-a]PYRIDINE-8-CARBOXAMIDE

[0120] Step 1. methyl 2,6-bis[(2,2-dimethylpropanoyl)amino]nicotinate

[0121] In a 5 L, 4-necked round bottom flask, immersed in ice-coldethanol-isopropanol (isopropanol 13%, −15° C.) bath, to a solution of2,6-bis[(2,2-dimethylpropanoyl)amino]pyridine (J. Am. Chem. Soc. 1986,108, 3310-3318, 126 g, 454 mmol) in anhydrous tetrahydrofuran (1.5 L)was added 2.66 M solution of n-buthyllithium in hexane (598 mL) dropwisefrom a dropping funnel (1 L) during the period of 6 h under nitrogenatmosphere (internal temperature was maintained at −15° C.˜−5° C.). Theresulting solution was stirred at 0° C. (internal temperature) for 12 hunder nitrogen atmosphere. The formation of yellowish precipitate wasnoticed. Then the suspension was cooled to −15° C., dimethyl carbonate(194 mL, 2.3 mmol) was added in one portion. The reaction solution wasstirred at 0° C. for 1 h, quenched with 1.5 L of 1 N aqueoushydrochloric acid, pH value was controlled to ˜4.5 by adding 1 N aqueoushydrochloric acid, then 600 mL of ethyl acetate was added. After thelayers were separated, the organic layer was washed with 1 L of 0.2 Naqueous NaOH (1 L) and brine (500 mL). Each aqueous layer was extractedwith ethyl acetate (300 mL) twice. Combined organic layer was dried oversodium sulfate (˜300 g) and concentrated. The residue was diluted withdiisopropylether (300 mL) and the solution was evaoprated to remove theresidual ethyl acetate azeotropically. The residue was dissolved withdiisopropylether (360 mL) at 60° C. with gentle stirring, and then thesmall portion of the crystalline of the desired product (˜5 mg) wasadded as seed. The formation of a pale yellow precipitate was noticed.The resulting suspension was cooled to room temperature (during theperiod of 2 h), and stirred at room temperature for 2 h. The suspensionwas filtered through paper filter, then the cake was washed withdiisopropylether (80 mL). The solid was dried under reduced pressure atroom temperature for 1 day to give the title compound (120 g, 358 mmol,79%) as a pale yellow solid.

[0122] MS (EI) m/z: 335 (M⁺) ¹H-NMR (CDCl₃) δ: 1.32 (9 H, s), 1.35 (9 H,s), 3.93 (3 H, s), 8.04 (1 H, d, J=8.8 Hz), 8.31 (1 H, d, J=8.8 Hz),9.32 (1 H, br s), 11.47 (1 H, br s).

[0123] Step 2. methyl5-chloro-2,6-bis[(2,2-dimethylpropanoyl)amino]nicotinate

[0124] To a solution of methyl2,6-bis[(2,2-dimethylpropanoyl)amino]nicotinate (EXAMPLE 1, Step 1, 186g, 555 mmol) in anhydrous N,N-dimethylformamide (930 mL) was added asolution of N-chlorosuccinimide (81.5 g, 610 mmol) in anhydrousN,N-dimethylformamide (560 mL) dropwise from a dropping funnel (1 L)during the period of 2.5 h at 70° C. (internal temperature) undernitrogen atmosphere. The resulting pale yellow solution was stirred at70° C. for 2 h and allowed to cool to room temperature. The reactionsolution was quenched with a solution of 250 g of ammonium chloride and100 g of sodium hydrogen sulfite in 3 L of water and extracted with amixture of ethyl acetate and hexane (3 L, 3:1). After the layers wereseparated, the organic layer was washed with water (2 L), dried oversodium sulfite (300 g) and evaporated. The residual pale yellow solidwas added isopropylether (1.4 L) and the resulting mixture was stirredat 60° C. for 2 h. After the mixture was cooled to room temperature, themixture was filtered through paper filter, and the cake was washed withisopropylether (200 mL), dried under reduced pressure at roomtemperature to give (153.9 g, 416 mmol) of the title compound as a whitesolid.

[0125] MS (ESI+) m/z: 370 (M+1) ¹H-NMR (CDCl₃) δ: 1.34 (18 H, s), 3.94(3 H, s), 8.30 (1 H, s), 8.51 (1 H, br s), 11.12 (1 H, brs).

[0126] Step 3. methyl 2,6-diamino-5-chloronicotinate

[0127] To a colorless solution of methyl5-chloro-2,6-bis[(2,2-dimethylpropanoyl)amino]-nicotinate (EXAMPLE 1,Step 2, 153.9 g, 416 mmol) in methanol (1.5 L) was added a solution ofpotassium tert-butoxide (185 g, 1.65 mol) in methanol (500 mL) dropwiseduring the period of 20 min at room temperature under nitrogenatmosphere. Dissolving potassium tert-butoxide in methanol wasexothermic, so potassium tert-butoxide must be added portionwise frompowder addition funnel to methanol during the period of 2 h withice-cold water bath. After the addition was completed, the reactionsolution was stirred at reflux temperature for 1 h under nitrogenatmosphere, and cooled to room temperature. The resulting suspension wasevaporated and ca. 1.3 L of methanol was removed (ca. 700 mL of methanolwas remained). To this mixture was added water (1.2 L) and stirred atroom temperature for 1 h with water bath (internal temperature wasmaintained at 20° C.), then the resulting suspension was filteredthrough paper filter and the pale yellow solid was dried under reducedpressure at 50° C. for 12 h to give 74.3 g (368.9 mmol, 89%) of thetitle compound as a pale yellow crystal. Rf value: 0.28 (ethylacetate/hexane=1:2).

[0128]¹H-NMR (DMSO-d₆) δ: 3.71 (3 H, s), 6.77 (2 H, br s), 6.94 (2 H, brs), 7.72 (1 H, s).

[0129] Step 4. methyl5-amino-6-chloro-2-methylimidazo[1,2-a]pyridine-8-carboxylate

[0130] A mixture of methyl 2,6-diamino-5-chloronicotinate (EXAMPLE 1,Step 3, 15 g, 74.4 mmol), bromoacetone (10.4 mL, 112 mmol) and sodiumiodide (16.7 g, 112 mmol) in methanol (700 mL) was stirred under refluxfor 22 h. Another 2.5 mL (33 mmol) of bromoacetone was added and thestirring was continued for 24 h. The reaction mixture was quenched withsaturated aqueous sodium carbonate and removed methanol in vacuo. Theresidue was extracted with ethyl acetate (250 mL×10) adding a smallamount of methanol to dissolve the organic solid. The organic extractswere dried over sodium sulfate and concentrated. Purification by columnchromatography on silica gel eluting with dichloromethane/methanol(20:1) gave a dark brown solid, which was washed with ethyl acetate andfiltered to afford 10.5 g (43.9 mmol, 59%) of the title compound as apale brown solid.

[0131] MS (FAB) m/z: 240 (M+1). ¹H-NMR (DMSO-d₆) δ: 2.34 (3 H, s), 3.80(3 H, s), 7.70 (2 H, br s), 7.83 (1 H, s), 7.85 (1H, s).

[0132] Step 5. methyl5-amino-6-chloro-2-methylimidazo[1,2-a]pyridine-8-carboxylic acid

[0133] A mixture of methyl5-amino-6-chloro-2-methylimidazo[1,2-a]pyridine-8-carboxylate (EXAMPLE1, Step 4, 10.5 g, 43.9 mmol,) and 1 N lithium hydroxide (87.7 mL, 87.7mmol) in methanol (100 mL) was stirred under reflux for 1 h. Afterremoval of the solvent in vacuo, the residue was suspended with waterand treated with 2 N hydrochloric acid to adjust to pH 4. The resultingsolid was filtered, washed with water and diethyl ether and dried invacuo with heating to give 9.5 g (42.2 mmol, 96%) of the title compoundas a brown solid.

[0134] MS (EI) m/z: 225 (M⁺). ¹H-NMR (DMSO-d₆) δ: 2.38 (3 H, s), 7.88 (1H, s), 7.92 (1 H, s), 8.00 (2 H, br s). A signal due to COOH was notobserved.

[0135] Step 6.5-amino-6-chloro-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-a]pyridine-8-carboxamide

[0136] To a suspension of5-amino-6-chloro-2-methylimidazo[1,2-a]pyridine-8-carboxylic acid(EXAMPLE 1, Step 5, 7.0 g, 31.0 mmol) in N,N-dimethylformamide (140 mL)was added 1,1′-carbonyldiimidazole (6.0 g, 37.2 mmol) at roomtemperature. After stirring for 5 min, the temperature was raised to 60°C. and the stirring was continued for 2.5 h. Another 2.5 g (15.5 mmol)of 1,1′-carbonyldiimidazole was added at room temperature and themixture was stirred at the temperature for 40 min and at 60° C. for 2 h.Then a N,N-dimethylformamide (25 mL) solutionof(1-isobutylpiperidin-4-yl)methylamine (Bioorg. Med. Chem. 1999, 7,2271-2281, 6.3 g, 37.2 mmol) was added at room temperature and thestirring was continued for 18 h. The mixture was quenched with water(165 mL). The resulting precipitate was collected by filtration andwashed with water (200 mL). The filtrate was extracted with ethylacetate (150 mL×2). The precipitate and the organic extracts werecombined and concentrated. The residue was purified by columnchromatography (basic silica gel) eluting with ethyl acetate/hexane (1:1to 2:1) to give a pale yellow solid (8.39 g), which was washed withdiethyl ether (200 mL) to give 7.3 g (19.4 mmol, 63%) of the titlecompound as a white solid.

[0137] MS (EI) m/z: 377(M⁺). m.p.: 216-219° C. IR (KBr) v: 3472, 3246,2951, 2920, 1638, 1607, 1562, 1545, 1437, 1321, 1265, 1148, 1101, 710cm⁻¹. ¹H-NMR (DMSO-d₆) δ: 0.82 (6 H, d, J=6.6 Hz), 1.18-1.31 (2 H, m),1.41-1.55 (1 H, m), 1.61-1.83 (5 H, m), 1.97 (2 H, d, J=7.2 Hz), 2.37 (3H, s), 2.78-2.81 (2 H, m), 3.28 (2 H, t, J=6.0 Hz), 7.58 (2 H, br s),7.86 (1 H, s), 7.88 (1 H, s), 9.92 (1 H, br). Anal. Calcd. forC₁₉H₂₈ClN₅O: C, 60.39; H, 7.47; N, 18.53. Found: C, 60.33; H, 7.68; N,18.43.

Example 2 5-AMINO-N-[(1-ISOBUTYLPIPERIDI-4-YL)METHYL]-2-METHYLIMIDAZO[1,2-a]PYRIDINE-8-CARBOXAMIDE

[0138] A mixture of5-amino-6-chloro-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-a]pyridine-8-carboxamide(EXAMPLE 1, Step 6, 134 mg, 0.36 mmol), 10% palladium charcoal (67 mg)and ammonium formate (224 mg, 3.6 mmol) in methanol (5 mL) was stirredat room temperature for 4 h. The mixture was filtered through a pad ofCelite and the filtrate was concentrated. The residue was treated with25% aqueous ammonia (10 mL), extracted with dichloromethane (20 mL×2)and washed with brine (20 mL). Removal of the solvent gave 92.4 mg (0.37mmol, 76%) of the title compound as a yellow amorphous powder.

[0139] MS (EI) m/z: 343(M⁺). IR (KBr) v: 3327, 3180, 2953, 2924, 1638,1558, 1516, 1431, 1290 cm⁻¹. ¹H-NMR (DMSO-d₆) δ: 0.83 (6 H, d, J=6.5Hz), 1.17-1.32 (2 H, m), 1.40-1.54 (1 H, m), 1.61-1.85 (5 H, m), 1.99 (2H, d, J=7.3 Hz), 2.36 (3 H, s), 2.79-2.83 (2 H, m), 3.25-3.29 (2 H, m),6.04 (1 H, d, J=8.1 Hz), 7.26 (2 H, br s), 7.68 (1 H, s), 7.85 (1 H, d,J=8.1 Hz), 10.00 (1 H, br). Anal. Calcd. forC₁₉H₂₉N₅O.0.05C₄H₈O₂.0.5H₂O: C, 64.62; H, 8.59; N, 19.62. Found: C,64.89; H, 8.64; N, 19.36.

Example 35-AMINO-6-CHLORO-N-{[1-(3,3-DIMETHYLBUTYL)PIPERIDIN4-YL]METHYL}-2-ETHYLIMIDAZO[1,2-a]PYRIDINE-8-CARBOXAMIDE

[0140] Step 1, methyl5-amino-6-chloro-2-ethylimidazo[1,2-a]pyridine-8-carboxylate

[0141] The title compound was prepared according to the proceduredescribed in the step 4 in EXAMPLE 1 from methyl2,6-diamino-5-chloro-3-pyridinecarboxylate (EXAMPLE 1, Step 3) and1-bromo-2-butanone.

[0142] MS (EI) m/z: 253 (M⁺). ¹H-NMR (DMSO-d₆) δ: 1.27 (3 H, t, J=7.5Hz), 2.72 (2 H, q, J=7.5 Hz), 3.80 (3 H, s), 7.72 (2 H, s), 7.86 (1 H,s), 7.87 (1 H, s).

[0143] Step 2,5-amino-6-chloro-2-ethylimidazo[1,2-a]pyridine-8-carboxylic acid

[0144] The title compound was prepared according to the proceduredescribed in the step 5 in EXAMPLE 1, from methyl5-amino-6-chloro-2-ethylimidazo[1,2-a]pyridine-8-carboxylate (EXAMPLE 3,Step 1).

[0145] MS (EI) m/z: 239 (M⁺). ¹H-NMR (DMSO-d₆) δ: 1.27 (3 H, t, J=7.2Hz), 2.74 (2 H, q, J=7.2 Hz), 7.88 (1 H, s), 7.95 (1 H, s). A signal dueto COOH was not observed.

[0146] Step 3. tert-butyl4-({[(5-amino-6-chloro-2-ethylimidazo[1,2-a]pyridin-8-yl)carbonyl]amino}methyl)piperidine-1-carboxylate

[0147] A mixture of5-amino-6-chloro-2-ethylimidazo[1,2-a]pyridine-8-carboxylic acid(EXAMPLE 3, Step 2, 10.00 g, 41.72 mmol), tert-butyl4-(aminomethyl)piperidine-1-carboxylate (J. Prugh, L. A. Birchenough andM. S. Egbertson, Synth. Commun., 1992, 22, 2357-60, 15.20 g, 70.93mmol), DEPC (10.76 mL, 70.93 mmol) and diisopropylethylamine (18.17 mL,104.4 mmol) in N,N-dimethylformamide (267 mL) was stirred at roomtemperature for 43 h. The solvent was removed by evaporation. Theresidue was basified with aqueous sodium bicarbonate (40 mL), andextracted with dichloromethane (5×100 mL). The combined extract waswashed with brine, dried over magnesium sulfate, and concentrated invacuo. Flash chromatography of the residue eluting withdichloromethane/methanol (100:1 to 20:1) afforded 19.08 g (90%) of thetitle compound as a yellow oil.

[0148]¹H-NMR (CDCl₃) δ: 1.35 (3 H, t, J=7.6 Hz), 1.45 (9 H, s),1.88-1.28 (5 H, m), 2.88-2.64 (2 H, m), 3.52-3.38 (2 H, m), 4.30-3.97 (4H, m), 5.17 (2 H, br s), 7.21 (1 H, s), 8.19 (1 H, s), 10.21 (1 H, bv).

[0149] Step 4.5-amino-6-chloro-2-ethyl-N-(piperidin-4-ylmethyl)imidazo[1,2-a]pyridine-8-carboxamide

[0150] To a stirred solution of tert-butyl4-({[(5-amino-6-chloro-2-ethylimidazo[1,2-a]-pyridin-8-yl)carbonyl]amino}methyl)piperidine-1-carboxylate(EXAMPLE 3, Step 3, 13.71 g, 31.44 mmol) in 10% hydrochloric acidmethanol solution (314 mL) was added concentrated hydrochloric acid (10mL). After stirring at room temperature for 26 h, the mixture wasconcentrated to about 50 mL in vacuo. The residue was basified with anexcess of sodium carbonate and then insoluble material was filtered off.The filtrate was concentrated azeotropically with ethanol and dilutedwith a mixture of dichloromethane and methanol (5:1, 200 mL). The formedinorganic solid was filtered off again. The filtrate was concentrated invacuo to give a pale yellow amorphous, which was crystallized fromethanol to afford 4.79 g (45%) of the title compound as an off-whitesolid. Furthermore, 5.09 g (48%) of the compound was obtained from themother liquid.

[0151] MS (ESI) m/z: 336.17 (M+H)⁺, 334.14 (M−H)⁻. m.p. (TG/DTA): 153°C. IR (KBr) v: 3387, 3300, 3188, 2964, 1639, 1605, 1562, 1514 cm⁻¹.¹H-NMR (DMSO-d₆) δ: 1.30-0.90 (2 H, m), 1.30 (3 H, t, J=7.6 Hz),1.74-1.50 (3 H, m), 2.55-2.36 (2 H, m), 2.75 (2 H, q, J=7.6 Hz),3.04-2.86 (2 H, m), 3.27 (2 H, t, J=5.9 Hz), 7.86 (1 H, s), 7.94 (1 H,s), 10.05-9.94 (1 H, m). Anal. Calcd. for C₁₆H₂₂ClN₅O.2.5H₂O.0.8EtOH: C,50.70; H, 7.49; N, 16.80. Found: C, 50.57; H, 7.27; N, 16.80.

[0152] Step 5.5-amino-6-chloro-N-{[1-(3,3-dimethylbutyl)piperidin-4-yl]methyl}-2-ethylimidazo[1,2-a]pyridine-8-carboxamide

[0153] To a stirred mixture of5-amino-6-chloro-2-ethyl-N-(piperidin-4-ylmethyl)imidazo[1,2-a]pyridine-8-carboxamide (EXAMPLE 3, Step 4, 450 mg, 1.34 mmol) and1-bromo-3,3-dimethylbutane (606 mg, 3.35 mmol) in N,N-dimethylfornamide(6 mL) were added potassium carbonate (648 mg, 4.69 mmol) and sodiumiodide (502 mg, 3.35 mmol). After stirring at 90° C. for 42 h, thereaction mixture was cooled and evaporated. The residue was diluted withdichloromethane (30 mL) and water (20 mL). The mixture was extractedwith dichloromethane (2×30 mL). The combined extract was washed withbrine, dried over magnesium sulfate, and concentrated. Flashchromatography (NH-silica gel) of the residue eluting with hexane/ethylacetate (1:1 to 1:2) afforded a brown solid (296 mg), which wasrecrystallized from ethyl acetate to give 191 mg (34%) of the titlecompound as a pale brown solid.

[0154] MS (ESI) m/z: 420 (M+H)⁺, 418 (M−H)⁻. m.p. (TG/DTA): 234° C. IR(KBr) v: 3136, 2947, 1636, 1607,1558 cm⁻¹. ¹H-NMR (CDCl₃) δ: 0.89 (9 H,s), 1.36 (3 H, t, J=7.5 Hz), 1.98-1.36 (9 H, m), 2.37-2.26 (2 H, m),2.83 (2 H, q, J=7.5 Hz), 3.02-2.92 (2 H, m), 3.45 (2 H, t, J=6.2 Hz),4.96 (2 H, bsv), 7.12 (1 H, s), 8.20 (1 H, s), 10.17 (1 H, bs). Anal.Calcd. for C₂₂H₃₄ClN₅O: C, 62.91; H, 8.16; N, 16.68. Found: C, 62.71; H,8.20; N, 16.62.

Example 45-AMINO-6-CHLORO-2-ETHYL-N-{[1-(2-METHOXY-2-METHYLPROPYL)PIPERIDIN-4-YL]METHYL}IMIDAZO[1,2-a]PYRIDINE-8-CARBOXAMIDE

[0155] Step 1, tert-butyl4-[(dibenzylamino)carbonyl]piperidine-1-carboxylate

[0156] To a stirred mixture of1-(tert-butoxycarbonyl)piperidine-4-carboxylic acid (J. Med. Chem. 1998,41, 2492-2502, 3.0 g, 13.1 mmol), dibenzylamine (2.5 mL, 13.1 mmol) anddiisopropylethylamine (3.4 mL, 19.7 mmol) in dichrolomethane (150 mL)was added PyBroP (bromo-tris-pyrrolidino-phosophoniumhexafluorophosphate) (6.1 g, 15.7 mmol) was added at 0° C. The mixturewas stirred at ambient temperature for 18 h and partitioned betweendichloromethane and water. After extraction with dichloromethane, thecombined organic phase was dried over magnesium sulfate andconcentrated. The residue was purified by flash column chromatography onsilica gel eluting with hexane/ethyl acetate (6:1) to afford 4.0 g (75%)of the title compound as a colorless amorphous powder.

[0157]¹H-NMR (CDCl₃) δ: 1.43 (9 H, s), 1.50-1.74 (4 H, m), 1.78-1.95 (2H, m), 2.58-2.75 (2 H, m), 4.45-4.51 (1 H, m), 7.11-7.44 (10 H, m).

[0158] Step 2. N,N-dibenzylpiperidine-4-carboxamide

[0159] To a stirred solution of tert-butyl4-[(dibenzylamino)carbonyl]piperidine-1-carboxylate (EXAMPLE 4, Step 1,4.0 g, 10.0 mmol) in methanol (550 mL) was added 4N HCl dioxane solution(80 mL, 320 mmol) at 0° C. The mixture was stirred for 6 h andevaporated. The resulting amorphous was dissolved in aqueous ammonia andthe mixture was extracted with dichloromethane. The combined extract wasdried over magnesium sulfate, and concentrated to afford 3.0 g (99%) ofthe title compound as a colorless amorphous powder.

[0160] MS (ESI) m/z: 309 (M+H)⁺, 307 (M−H)⁻.

[0161] Step 3. N,N-dibenzyl-N-(piperidin-4-ylmethyl)amine

[0162] To a suspension of lithium aluminum hydride (min.80%, 1.50 g,40.0 mmol) in tetrahydrofuran (50 ml) was added dropwise a solution ofN,N-dibenzylpiperidine-4-carboxamide (EXAMPLE 4, Step 2, 3.08 g, 10.0mmol) in tetrahydrofuran (50 ml) at 0° C. over 15 min. The mixture wasstirred at 0° C. for 30 min and at 40° C. for 4 h. After cooling to 0°C., water (3.3 ml), 15% NaOH aqueous solution (3.3 ml), and then water(10 ml) were carefully added dropwise. The resulting mixture wasfiltered through a pad of Celite and the filtrate was concentrated invacuo to give 2.85 g (97%) of the title compound as a pale yellow oil.

[0163] MS (ESI) m/z: 295 (M+H)⁺, 293 (M−H)⁻. ¹H-NMR (CDCl₃) δ: 0.90-1.10(2 H, m), 1.70-1.92 (4 H, m), 2.20 (2 H, d, J=7.2 Hz), 2.78 (1 H, s),2.86 (2 H, d, J=11.5 Hz), 3.48 (4 H, s), 7.16-7.35 (10 H, m).

[0164] Step 4.1-{4-[(dibenzylamino)methyl]piperidin-1-yl}-2-methylpropan-2-ol

[0165] A mixture of N,N-dibenzyl-N-(piperidin-4-ylmethyl)amine (EXAMPLE4, Step 3, 3.3 g, 11.21 mmol) and 2,2-dimethyloxirane (12.1 mL, 134.5mmol) in methanol (40 mL) and tetrahydrofuran (5 mL) was heated at 40°C. with stirring for 17 h. The volatile components were removed and theresidue was purified by flash column chromatography on amine gel elutingwith hexane/ethyl acetate (50:1) to afford 3.0 g (73%) of the titlecompound as a colorless amorphous.

[0166] MS (ESI) m/z: 367 (M+H)⁺.

[0167] Step 5.N,N-dibenzyl-N-{[1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methyl}amine

[0168] To a suspension of sodium hydride (abt. 60% in mineral oil, 342mg, 8.6 mmol) in a mixture of tetrahydrofuran (20 mL) andN,N-dimethylformamide (10 mL) was added a solution of1-{4-[(dibenzylamino)methyl]piperidin-1-yl}-2-methylpropan-2-ol (EXAMPLE4, Step 4, 3.0 g, 8.2 mmol) in tetrahydrofuran (20 ml) at 0° C. Aferbeing stirred at the same temperature for 30 min, 0.53 mL (8.6 mmol) ofiodomethane was added to the mixture. The mixture was stirred at ambienttemperature for 3 days. The mixture was partitioned between ethylacetate and water. After extraction with ethyl acetate, the combinedorganic phase was dried over magnesium sulfate, and concentrated. Theresidue was purified by flash column chromatography on amine gel elutingwith hexane/ethyl acetate (100:1) to afford 0.76 g (24%) of the titlecompound as colorless amorphous.

[0169] MS (ESI) m/z: 381 (M+H)⁺. ¹H-NMR (CDCl₃) δ: 1.12 (6 H, s),0.99-1.19 (2 H, m), 1.43-1.60 (1 H, m), 1.69-1.74 (2 H, m), 2.01-2.11 (2H, m), 2.11-2.26 (4 H, m), 2.84-2.91 (2 H, m), 3.18 (3 H, s), 3.50 (3 H,s), 7.18-7.37 (10 H, m).

[0170] Step 6. [1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methylamine

[0171] To a solution ofN,N-dibenzyl-N-{[1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methyl}amine(EXAMPLE 4, Step 5, 756 mg, 1.85 mmol) and ammonium formate (583 mg,9.24 mmol) in methanol (40 mL) and water (15 mL) was added 10% palladiumon carbon (185mg) at ambient temperature. The mixture was heated at 80°C. for 6 h. After cooling, the mixture was filtered through a pad ofCelite and the filtrate was concentrated in vacuo. The obtained residuewas partitioned between dichlorometane and aqueous ammonia. Afterextraction with dichloromethane, the combined organic extract was driedover magnesium sulfate and concentrated to give 275 mg (66%) of thetitle compound as a pale yellow oil.

[0172]¹H-NMR (CDCl₃) δ: 1.15 (6 H, s), 1.17-1.26 (2 H, m), 1.58-1.68 (1H, m), 2.05-2.19 (2 H, m), 2.28 (2 H, s), 2.53-2.56 (2 H, m), 2.90-2.98(2 H, m), 3.20 (3 H, s

[0173] Step 7.5-amino-6-chloro-2-ethyl-N-{[1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methyl}imidazo[1,2-a]pyridine-8-carboxamide

[0174] The title compound was prepared according to the proceduredescribed in the step 6 in EXAMPLE 1, using5-amino-6-chloro-2-ethylimidazo[1,2-a]pyridine-8-carboxylic acid(EXAMPLE 3, Step 2) and[1-(2-methoxy-2-methylpropyl)piperidin4-yl]methylamine (EXAMPLE 4, Step6).

[0175] MS (ESI) m/z: 422 (M+H)⁺, 420(M−H)⁻. m.p.: 211° C. IR (KBr) v:3466, 3250, 2955, 2930, 2918, 1632, 1620, 1600, 1545, 1437, 1319, 1268,1146, 1105, 998 cm⁻¹. ¹H-NMR (CDCl₃) δ: 1.16 (6 H, s), 1.35 (3 H, t,J=7.5 Hz), 1.71-1.76 (2 H, m), 2.29 (2 H, s), 2.82 (2 H, q, J=7.5 Hz),2.46 (3 H, s), 2.93-2.97 (2 H, m), 3.43 (2 H, t, J=6.4 Hz), 4.97 (2 H,brs), 7.14 (1 H, s), 8.19 (1 H, s), 10.08 (1 H, br). Anal. Calcd. forC₂₁H₃₂ClN₅O₂.0.5H₂O: C, 59.14; H, 7.68; N, 16.42. Found: C, 59.03; H,7.62; N, 16.24.

Example 55-AMINO-6-CHLORO-2-METHYL-N-{[1-(2-METHOXY-2-METHYLPROPYL)PIPERIDIN-4-YL]METHYL}IMIDAZO[1,2-a]PYRIDINE-8-CARBOXAMIDE

[0176] The title compound was prepared according to the proceduredescribed in the step 6 in EXAMPLE 1 from5-amino-6-chloro-2-methylimidazo[1,2-a]pyridine-8-carboxylic acid(EXAMPLE 1, Step 5) and[1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methylamine (EXAMPLE 4, Step6).

[0177] MS (ESI) m/z: 408 (M+H)⁺, 406 (M−H)⁻. m.p.: 211° C. IR (KBr) v:3470, 3342, 3208, 2940, 2918, 1655, 1601, 1555, 1545, 1437, 1319, 1288,1266, 1147 cm⁻¹. ¹H-NMR (CDCl₃) δ: 1.16 (6 H, s), 1.39-1.47 (2 H, m),1.71-1.76 (2 H, m), 2.16 (2 H, t, J=11.0 Hz), 2.29 (2 H, s), 2.46 (3 H,s), 2.93-2.97 (2 H, m), 3.20 (3 H, s), 3.43 (2 H, t, J=6.4 Hz), 4.97 (2H, br s), 7.14 (1 H, s), 8.19 (1 H, s), 10.08 (1 H, br s). Anal. Calcd.for C₂₁H₃₂ClN₅O₂: C, 58.89; H, 7.41; N, 17.17. Found: C, 58.62; H, 7.38;N, 16.93.

Example 65-AMINO-6-CHLORO-N-{[1-(2,2-DIMETHYLPROPYL)PIPERIDIN4-YL]METHYL}-2-ETHYLIMIDAZO[1,2-a]PYRIDINE-8-CARBOXYAMIDE

[0178] Step 1. 1-(2,2-dimethylpropyl)piperidine-4-carboxyamide

[0179] To a solution of isonipecotamide (2 g, 15.6 mmol) andpivalaldehyde (2.0 mL, 18.7 mmol) in tetrahydrofuran (200 mL) was addedtitanium(IV) isopropoxide (4.6 mL, 15.6 mmol) and the mixture wasstirred at room temperature for 21 h under nitrogen. Solvent wasremoved, the residue was dissolved in ethanol (60 mL) and sodiumcyanoborohydride (1.6 g, 23.4 mmol) was added at room temperature. Afterstirring for 89 h, water (30 mL) was added, obtained precipitate wasremoved by filtration and the filtrate was concentrated. The residue wastreated with water (30 mL) basified with 2 N sodium hydroxide, extractedwith dichloromethane (30 mL×3) and washed with brine (30 mL). Theorganic extracts were dried over sodium sulfate and concentrated to givea white solid, which was purified by flash column chromatography onsilica gel eluting with dichloromethane/methanol/25% ammonia solution(20:1:0.1) to affoad 715 mg (23%) of the title compound as a whitesolid.

[0180] MS (ESI) m/z: 199 (M+1)⁺. ¹H-NMR (CDCl₃) δ: 0.82 (9 H, s),1.52-1.60 (4 H, m), 1.91-2.01 (3 H, m), 2.09-2.18 (2 H, m), 2.72-2.76 (2H, m), 6.70 (1 H, br s), 7.24 (1 H, br s).

[0181] Step 2. {[1-(2,2-dimethylpropyl)piperidin-4-yl]methyl}amine

[0182] To a suspension of lithium aluminum hydride (342 mg, 7.2 mmol) intetrahydrofuran (15 mL) was added a tetrahydrofuran solution (15 mL) of1-(2,2-dimethylpropyl)piperidine-4-carboxyamide (EXAMPLE 6, Step 1, 715mg, 3.6 mmol) at 0° C. The mixture was stirred at 40° C. for 2 h, cooledto room temperature and quenched with sodium sulfate decahydrate andpotassium fluoride. Filtration through a pad of Celite and concentrationof the filtrate gave a crude of the title compound (785 mg) as acolorless oil.

[0183] MS (ESI) m/z: 185 (M+1)⁺. ¹H-NMR (CDCl₃) δ: 0.85 (9 H, s),1.11-1.28 (2 H, m), 1.49-1.86 (5 H, m), 2.12-2.19 (2 H, m), 2.54-2.56 (2H, m), 2.78-2.81 (2 H, m), 3.67-3.69 (2 H, m).

[0184] Step 3.5-amino-6-chloro-N-{[1-(2,2-dimethylpropyl)piperidin-4-yl]methyl}-2-ethylimidazo[1,2-a]pyridine-8-carboxyamide

[0185] The title compound was prepared according to the proceduredescribed in the Step 6 in EXAMPLE 1, from5-amino-6-chloro-2-ethylimidazo[1,2-a]pyridine-8-carboxylic acid(EXAMPLE 3, Step 2) and{[1-(2,2-dimethylpropyl)piperidin-4-yl]methyl}amine (EXAMPLE 6, Step 2).

[0186] MS (ESI) m/z: 406 (M+1)⁺. m.p. (TG/DTA): 252° C. IR (KBr) v:3470, 3142, 3086, 2949, 1636, 1605, 1578, 1560, 1543, 1516, 1466, 1358,1339, 1271, 1229 cm⁻¹. ¹H-NMR (CDCl₃) δ: 0.85 (9 H, s), 1.36 (3 H, t,J=7.5 Hz), 1.37-1.49 (2 H, m), 1.52-1.66 (1 H, m), 1.71-1.75 (2 H, m),2.02 (2 H, s), 2.16-2.24 (2 H, m), 2.80-2.87 (4 H, m), 3.41-3.45 (2 H,m), 5.00 (2 H, br s), 7.16 (1 H, s), 8.20 (1 H, s), 10.17 (1 H, br).Anal. Calcd. for C21H32ClN5O: C, 62.13; H, 7.95; N, 17.25. Found: C,61.92; H, 7.94; N, 17.06.

Example 75-AMINO-6-CHLORO-N-{[1-(2,2-DIMETHYLPROPYL)PIPERIDIN-4-YL]METHYL}-2-METHYLIMIDAZO[1,2-a]PYRIDINE-8-CARBOXYAMIDE

[0187] The title compound was prepared according to the proceduredescribed in the Step 6 in EXAMPLE 1, from5-amino-6-chloro-2-methylimidazo[1,2-a]pyridine-8-carboxylic acid(EXAMPLE 1, Step 5) and{[1-(2,2-dimethylpropyl)piperidin-4-yl]methyl}amine (EXAMPLE 6, Step 2).

[0188] MS (ESI) m/z: 392 (M+1)⁺. m.p. (TG/DTA): 256° C. IR (KBr) v:3302, 3144, 2951, 1638, 1605, 1564, 1543, 1516, 1433, 1321, 1285, 1267,1231 cm⁻¹. ¹H-NMR (DMSO-d₆) δ: 0.82 (9 H, s), 1.23-1.42 (3 H, m),1.60-1.64 (2 H, m), 2.01 (2 H, s), 2.12-2.19 (2H, m), 2.37 (3 H, s),2.74-2.78 (2 H, m), 3.26-3.30 (2 H, m), 7.57 (2 H, br s), 7.85 (1 H, s),7.87 (1 H, s), 9.92 (1 H, br). Anal. Calcd. for C20H30ClN5O.0.1H2O: C,61.01; H, 7.73; N, 17.79. Found: C, 60.67; H, 7.68; N, 17.53.

Example 85-amino-6-chloro-N-{[1-(3-methoxy-3-methylbutyl)piperidin-4-yl]methyl}2-methylimidazo[1,2-a]pyridine-8-carboxamide

[0189] Step 1. tert-butyl4-({[(5-amino-6-chloro-2-methylimidazo[1,2-a]pyridin-8-yl)carbonyl]amino}methyl)piperidine-1-carboxylate

[0190] The title compound was prepared, according to the proceduredescribed in the step 6 of EXAMPLE 1, from5-amino-6-chloro-2-methylimidazo[1,2-a]pyridine-8-carboxylic acid(EXAMPLE 1, Step 5) and tert-butyl4-(aminomethyl)piperidine-1-carboxylate (J. Prugh, L. A. Birchenough andM. S. Egbertson, Synth. Commun., 1992, 22, 2357-60).

[0191] MS (EI) m/z: 421(M⁺). ¹H-NMR (CDCl₃) δ: 1.06-1.84 (14 H, m), 2.44(3 H, s), 2.58-2.85 (2 H, m), 3.45-3.49 (2 H, m), 4.00-4.22 (2 H, m),5.84 (2 H, s), 7.34 (1 H, s), 8.17 (1 H, s), 10.17 (1 H, br t, J=5.7Hz).

[0192] Step 2.5-amino-6-chloro-2-methyl-N-(piperidin-4-ylmethyl)imidazo[1,2-a]pyridine-8-carboxyamidedihydrochloride

[0193] A mixture of tert-butyl4-({[(5-amino-6-chloro-2-methylimidazo[1,2-a]pyridin-8-yl)carbonyl]amino}methyl)piperidine-1-carboxylate(EXAMPLE 8, Step 1, 15.1 g, 35.8 mmol) and conc. hydrochloric acid (5mL) in 10% hydrochloric acid methanol solution (150 mL) was stirred atroom temperature for 12 h. The solvent was removed to 30 mL in vacuo andto the residue was added diethyl ether (100 mL). Obtained precipitatewas collected by filtration and washed with diethyl ether to give 13.9 g(98%) of the title compound as a pale yellow solid.

[0194] MS (ESI) m/z: 322(M+1)⁺. ¹H-NMR (DMSO-d₆) δ: 1.39-1.53 (2 H, m),1.80-1.91 (3 H, m), 2.45 (3 H, s), 2.69-2.89 (2 H, m), 3.22-3.26 (4 H,m), 8.38-9.13 (8 H, m).

[0195] Step 3.5-amino-6-chloro-N-{[1-(3-methoxy-3-methylbutyl)piperidin-4-yl]methyl}2-methylimidazo[1,2-a]pyridine-8-carboxamide

[0196] The title compound was prepared according to the proceduredescribed in the Step 5 in EXAMPLE 3 from5-amino-6-chloro-2-methyl-N-(piperidin-4-ylmethyl)imidazo[1,2-a]pyridine-8-carboxyamidedihydrochloride (EXAMPLE 8, Step 2) and1-iodo-3-methoxy-3-methylbutane*.

[0197] MS (ESI) m/z: 422 (M+1)⁺. m.p. (TG/DTA): 199° C. IR (KBr) v:3499, 3325, 3182, 2926, 1657, 1620, 1601, 1572, 1547, 1514, 1431, 1323,1261, 1078, 721 cm⁻¹. ¹H-NMR (CDCl₃) δ: 1.16 (6 H, s), 1.37-1.49 (2 H,m), 1.60-1.72 (3 H, m), 1.82-1.86 (2 H, m), 1.91-1.99 (2 H, m),2.35-2.40 (2 H, m), 2.46 (3 H, s), 2.95-2.99 (2 H, m), 3.18 (3 H, s),3.43-3.47 (2 H, m), 5.03 (2 H, br s), 7.15 (1 H, s), 8.19 (1 H, s),10.09 (1 H, br). Anal. Calcd. for C21H32ClN5O2.0.2H2O: C, 59.27; H,7.67; N, 16.46. Found: C, 59.00; H, 7.66; N, 16.19.

[0198] Preparation of 1-iodo-3-methoxy-3-methylbutane

[0199] To a solution of 3-methoxy-3-methyl-1-butanol (3 g, 25.3 mmol) indichloromethane (100 mL) were added triphenylphosphine (7.3 g, 27.9mmol), imidazole (1.9 g, 27.9 mmol) and iodine (7.1 g, 27.9 mmol) at 0°C. The mixture was stirred at 0° C. for 3 h. Aqueous sodium sulfite (5mL) and aqueous sodium hydrogen carbonate (100 mL) were added and themixture was extracted with dichloromethane (20 mL×3). After removal ofsolvent, the residue was suspended to hexane and filtered. The filtratewas concentrated. Flash chromatography of the residue eluting withhexane/ethyl acetate (100:1) gave 684 mg (9%) of the title compound as apale yellow oil.

[0200]¹H-NMR (CDCl₃) δ: 1.15 (6 H, s), 2.11-2.17 (2 H, m), 3.15-3.21 (2H, m), 3.18 (3 H, s). R_(f): 0.3 (hexane).

Example 95-amino-6-chloro-N-{[1-(3-methoxy-2,2-dimethylpropyl)piperidin-4-yl]methyl}2-methylimidazo[1,2-a]pyridine-8-carboxamide

[0201] Step 1.{[1-(3-methoxy-2,2-dimethylpropyl)piperidin-4-yl]methyl}amine

[0202] A mixture of isonipecotamide (1.0 g, 8.0 mmol),3-methoxy-2,2-dimethylpropanoic acid (Bulletin of the Chemical Societyof Japan 2001, 74, 1695-1702, 1.1 g, 8.0 mmol),2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate(HBTU, 3.3 g, 8.8 mmol) and N,N-diisopropylethylamine (1.5 mL, 8.8 mmol)in N,N-dimethylformamide (8 mL) was stirred at room temperature for 18h. Water (8 mL) was added and the mixture was extracted with ethylacetate (20 mL×6). Removal of solvent gave a crude of1-(3-methoxy-2,2-dimethylpropanoyl)piperidine-4-carboxamide as a brownoil, which was dissolved in tetrahydrofuran (15 mL) and added to asuspension of lithium aluminum hydride (2.26 g, 47.7 mmol) intetrahydrofuran (15 mL) at 0° C. The mixture was stirred at 40° C. for 3h and quenched with sodium sulfate decahydrate and potassium fluoride.Filtration through a pad of Celite and concentration of the filtrategave 925 mg (54%) of the title compound as a colorless oil.

[0203] MS (ESI) m/z: 215 (M+1)⁺. ¹H-NMR (CDCl₃) δ: 0.83 (6 H, s),1.13-1.32 (2 H, m), 1.52-1.80 (3 H, m), 2.12-2.24 (4 H, m), 2.53-2.55 (2H, m), 2.74-2.78 (2 H, m), 3.09 (2 H, s), 3.30 (3 H, s). A signal due toNH2 was not observed.

[0204] Step 2.5-amino-6-chloro-N-{[1-(3-methoxy-2,2-dimethylpropyl)piperidin4-yl]methyl}2-methyl-imidazo[1,2-a]pyridine-8-carboxamide

[0205] The title compound was prepared according to the proceduredescribed in the Step 6 in EXAMPLE 1 from5-amino-6-chloro-2-methylimidazo[1,2-a]pyridine-8-carboxylic acid(EXAMPLE 1, Step 5) and{[1-(3-methoxy-2,2-dimethylpropyl)piperidin4-yl]methyl}amine (EXAMPLE 9,Step 1).

[0206] MS (ESI) m/z: 422 (M+1)⁺. m.p. (TG/DTA): 199° C. IR (KBr) v:3309, 3152, 2922, 2868, 1638, 1603, 1560, 1545, 1512, 1425, 1321, 1111,718 cm⁻¹. ¹H-NMR (CDCl₃) δ: 0.83 (6 H, s), 1.34-1.46 (2 H, m), 1.53-1.65(1 H, m), 1.70-1.73 (2 H, m), 2.13 (2 H, s), 2.18-2.25 (2 H, m), 2.47 (3H, s), 2.76-2.80 (2 H, m), 3.09 (2 H, s), 3.30 (3 H, s), 3.41-3.46 (2 H,m), 4.98-5.07 (2 H, m), 7.16-7.19 (1 H, m), 8.20 (1 H, s), 10.09 (1 H,br). Anal. Calcd. for C21H32ClN5O2: C, 59.77; H, 7.64; N, 16.60. Found:C, 59.47; H, 7.65; N, 16.55.

[0207] All publications, including but not limited to, issued patents,patent applications, and journal articles, cited in this application areeach herein incorporated by reference in their entirety.

1. A compound of the formula (I):

or a pharmaceutically acceptable salt thereof, wherein R¹ represents ahydrogen atom or a halogen atom; R² represents a methyl group or anethyl group; R³ represents a branched alkyl group having from 3 to 6carbon atoms or an alkyl group having from 3 to 6 carbon atomssubstituted by an alkoxy group having from 1 to 6 carbon atoms; with theproviso that when the terminal carbon atom of said alkyl group of R³ issubstituted by said alkoxy group, said alkyl group is a branched alkylgroup.
 2. The compounds of claim 1, wherein R¹ represents a hydrogenatom or a chlorine atom.
 3. The compounds of claim 1, wherein R¹represents a chlorine atom.
 4. The compounds of any one of claims 1 to3, wherein R³ represents an iso-butyl group, a tert-butylethyl group;and said alkyl group of R³ is optionally substituted by a methoxy group.5. The compound of claim 1, which is5-amino-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-a]pyridine-8-carboxamide.6. The compound of claim 1, which is5-amino-6-chloro-N-{[1-(3,3-dimethylbutyl)piperidin-4-yl]methyl}-2-ethylimidazo[1,2-a]pyridine-8-carboxamide.7. The compound of claim 1, which is5-amino-6-chloro-2-ethyl-N-{[1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methyl}imidazo[1,2-a]pyridine-8-carboxamide.8. The compound of claim 1, which is5-amino-6-chloro-2-methyl-N-{[1-(2-methoxy-2-methylpropyl)piperidin-4-yl]methyl}imidazo[1,2-a]pyridine-8-carboxamide.9. The compound of claim 1, which is5-amino-6-chloro-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-a]pyridine-8-carboxamide.10. A pharmaceutical composition for the treatment or prevention ofgastroesophageal reflux disease, gastrointestinal disease, gastricmotility disorder, upper gut motility disorder, non-ulcer dyspepsia,functional dyspepsia, irritable bowel syndrome, constipation, dyspepsia,esophagitis, gastroesophageral disease, nausea, central nervous systemdisease, alzheimers disease, cognitive disorder, emesis, migraine,neurological disease, pain, ischaemic stroke, anxiety or cardiovasculardisorder, which comprises a therapeutically effective amount of acompound of the formula (I):

or a pharmaceutically acceptable salt thereof, wherein R¹ represents ahydrogen atom or a halogen atom; R2 represents a methyl group or anethyl group; R³ represents a branched alkyl group having from 3 to 6carbon atoms or an alkyl group having from 3 to 6 carbon atomssubstituted by an alkoxy group having from 1 to 6 carbon atoms; with theproviso that when the terminal carbon atom of said alkyl group of R³ issubstituted by said alkoxy group, said alkyl group is a branched alkylgroup.
 11. A method for the treatment or prevention of diseaseconditions mediated by 5-HT₄ receptor activity, in a mammalian subject,which comprises administering to said subject a therapeuticallyeffective amount of a compound of the formula (I):

or a pharmaceutically acceptable salt thereof, wherein R¹ represents ahydrogen atom or a halogen atom; R² represents a methyl group or anethyl group; R³ represents a branched alkyl group having from 3 to 6carbon atoms or an alkyl group having from 3 to 6 carbon atomssubstituted by an alkoxy group having from 1 to 6 carbon atoms; with theproviso that when the terminal carbon atom of said alkyl group of R³ issubstituted by said alkoxy group, said alkyl group is a branched alkylgroup.
 12. A method for the treatment or prevention of gastroesophagealreflux disease, gastrointestinal disease, gastric motility disorder,upper gut motility disorder, non-ulcer dyspepsia, functional dyspepsia,irritable bowel syndrome, constipation, dyspepsia, esophagitis,gastroesophageral disease, nausea, central nervous system disease,alzheimers disease, cognitive disorder, emesis, migraine, neurologicaldisease, pain, ischaemic stroke, anxiety or cardiovascular disorder,which comprises administering to said subject a therapeuticallyeffective amount of a compound of the formula (I):

or a pharmaceutically acceptable salt thereof,wherein R¹ represents ahydrogen atom or a halogen atom; R2 represents a methyl group or anethyl group; R³ represents a branched alkyl group having from 3 to 6carbon atoms or an alkyl group having from 3 to 6 carbon atomssubstituted by an alkoxy group having from 1 to 6 carbon atoms; with theproviso that when the terminal carbon atom of said alkyl group of R³ issubstituted by said alkoxy group, said alkyl group is a branched alkylgroup.